Republicans, in their brief, urged the high court to rule on the validity of the 2012 appointments, while arguing that Obama overstepped his bounds. 

"The president's decision to circumvent the American people by installing his appointees at a powerful federal agency while the Senate was continuing to hold sessions, and without obtaining the advice and consent of the Senate, is an unprecedented power grab," Senate Republican Leader Mitch McConnell said in a written statement. "We will demonstrate to the Court how the president's unconstitutional actions fundamentally endanger the Congress's role in providing a check on the excesses of the executive branch." 

The brief itself was submitted by attorney Miguel Estrada, whom the Republicans retained for work on this case. 

Estrada wrote that Obama's actions "would radically reshape the constitutional structure" if allowed to stand. 

"If he can override Senate procedures and second-guess its account of its actions, there is no telling what mischief he can achieve," he wrote. 

At issue are so-called recess appointments, a tactic used by presidents of both parties in the past. 

But a federal appeals court ruled earlier this year that the president made appointments to the NLRB when the Senate was not technically in recess, and therefore the appointments were invalid. 

A second appeals court ruled in May that another NLRB appointment from 2010 was also made when the Senate was merely adjourned. The court again ruled that the appointment was invalid.   

The administration argues that invalidating these appointments would invalidate recess appointments going back 100 years. 

But Republicans, and the business battling the NLRB in the prior case, argue that Obama has stretched his authority. 

The Obama administration had earlier appealed the January decision to the Supreme Court.

Republicans, in their brief, urged the high court to rule on the validity of the 2012 appointments, while arguing that Obama overstepped his bounds. 

"The president's decision to circumvent the American people by installing his appointees at a powerful federal agency while the Senate was continuing to hold sessions, and without obtaining the advice and consent of the Senate, is an unprecedented power grab," Senate Republican Leader Mitch McConnell said in a written statement. "We will demonstrate to the Court how the president's unconstitutional actions fundamentally endanger the Congress's role in providing a check on the excesses of the executive branch." 

The brief itself was submitted by attorney Miguel Estrada, whom the Republicans retained for work on this case. 

Estrada wrote that Obama's actions "would radically reshape the constitutional structure" if allowed to stand. 

"If he can override Senate procedures and second-guess its account of its actions, there is no telling what mischief he can achieve," he wrote. 

At issue are so-called recess appointments, a tactic used by presidents of both parties in the past. 

But a federal appeals court ruled earlier this year that the president made appointments to the NLRB when the Senate was not technically in recess, and therefore the appointments were invalid. 

A second appeals court ruled in May that another NLRB appointment from 2010 was also made when the Senate was merely adjourned. The court again ruled that the appointment was invalid.   

The administration argues that invalidating these appointments would invalidate recess appointments going back 100 years. 

But Republicans, and the business battling the NLRB in the prior case, argue that Obama has stretched his authority. 

The Obama administration had earlier appealed the January decision to the Supreme Court.

Earlier in the morning, he and first lady Michelle Obama hosted a breakfast at the White House with "Gold Star" families of service members who have been killed.

Another wreath-laying ceremony was at Franklin D. Roosevelt Four Freedoms Park on the southern tip of Roosevelt Island in New York City. The park is a tribute to President Roosevelt's famous speech calling for all people to enjoy freedom of speech, freedom of worship, freedom from want and freedom from fear.

Mayor Michael Bloomberg joined military leaders and others at the Soldiers' and Sailors' Monument in Manhattan. He later encouraged New Yorkers to celebrate the day and the good weather but also "remember the sacrifice that was made so that we could be here."

At the National World War II Museum in New Orleans, about 20 bicyclists clustered around veteran and museum volunteer Tom Blakey. The paratrooper in the 82nd Airborne Division jumped at Normandy on D-Day -- June 6, 1944 -- and in May 1945 helped liberate the work camp at Wobbelin in northwest Germany.

"Most of us wondered why we were there, killing people and being killed," he said. "We didn't do anything to deserve it. When we got to that camp and saw what was there, the lights came on."

The cycling group makes regular weekend training runs, and on Monday started a Memorial Day ride about seven miles away at the national cemetery in Chalmette, where the Battle of New Orleans -- the last in the War of 1812 -- was fought.

"I'm glad I took this ride to hear a personal story," Scott Gumina, 41, said. "Hearing one man's account of his personal experience was pretty impressive to me."

In South Sioux City, Neb., a statue honoring a Navy dog handler was unveiled in his hometown. The statue of John Douangdara (dwung-DEHR'-ah) and his dog, Bart, is part of a five-acre dog park that's named for Douangdara. Petty Officer 1st Class Douangdara died along with 29 other Americans in August 2011 when a military helicopter was shot down in Afghanistan.

Across much of New England, several days of heavy rain gave way to sunny skies for parades in towns large and small.

In Portland, Maine, kids and even pets displayed the Stars and Stripes as veterans, youth groups law enforcement officials and civic organizations paraded to Monument Square to the tunes of a marching band, sirens from a police car and the rumble of motorcycles.

"It's a very important day, not only for the Veteran of Foreign Wars but every veteran organization, every branch of the service, and every patriot in general -- every American. This day is hugely significant and should never be forgotten," said David Olson, 66, of Portland, the VFW's state senior vice commander.

For some veterans, it was a somber event.

Richard Traiser, a Marine injured when his tank came under attack in Vietnam, helped deliver a three-volley salute with the Marine Corps League.

Memorial Day gives those who served an opportunity to get together and remember friends who didn't make it.

"I think about them a lot, especially the people I lost in my platoon," Traiser said. "I don't dwell on it in a morbid way, but it's on your mind."

In Connecticut, a Waterford man who was killed in the Vietnam War was honored with a hometown park area named for him. Arnold E. Holm Jr., nicknamed "Dusty," was killed when his helicopter was shot down on June 11, 1972.

In suburban Boston, veterans gathered in a park to mark Memorial Day this year rather than hold a parade because of failing health and dwindling numbers. The city of Beverly called off its parade because so few veterans would be able to march. The parade has been a fixture in the town since the Civil War.

In Atlanta, a dedication of the History Center's redone Veterans Park was scheduled for early evening. Soil from major battlefields will be scattered by veterans around the park's flagpole.

The holiday weekend also marked the traditional start of the U.S. vacation season. AAA, one of the nation's largest leisure travel agencies, expected 31.2 million Americans to hit the road over the weekend, virtually the same number as last year. Gas prices were about the same as last year, up 1 cent to a national average of $3.65 a gallon Friday.

At the American Airpower Museum on Long Island, N.Y., a program honored Women Air Service Pilots, or WASPs, who tested and ferried completed aircraft from factories to bases during World War II. Thirty-eight died during the war, including Alice Lovejoy of Scarsdale, N.Y., who was killed on Sept. 13, 1944, in a midair collision over Texas.

"It's very important that we recognize not only their contribution to American history, but women's history," said Julia Lauria-Blum, curator of the WASP exhibit at the museum. "These women really blazed a path; they were pioneers for women's aviation. And most important, they gave their lives serving their country and must be honored like anyone else on Memorial Day."