"She was asked to cover it up. She did not," said Sgt. Kimberly Schneider, U.S. Capitol Police spokeswoman.

House rules bar demonstrations in the galleries.

On Wednesday, U.S. Rep. Bill Young, R-Florida, spoke on the House floor saying his wife, Beverly, had been "ordered to leave" the gallery during the speech for wearing a shirt that said, "Support Our Troops."

Young, an 18-term congressman, held up his wife's shirt during his remarks, speaking with anger and emotion about her treatment.

"She has a real passion for our troops, and she shows it in many, many ways," Young said.

"And most members in this House know that, but because she had on a shirt, that someone didn't like, that said, 'Support Our Troops,' she was kicked out of this gallery while the president was speaking and encouraging Americans to support our troops. Shame. Shame."

Sheehan held 4 hours

Sheehan was arrested around 8:30 p.m. ET Tuesday on charges of unlawful conduct, a misdemeanor that carries a maximum penalty of a year in jail, Capitol Police said.

She was handcuffed and held in the Capitol building until she was driven to the Capitol Police headquarters for booking. According to her blog, she was released about four hours after her arrest.

Sheehan, who became a vocal war opponent after her son was killed in Iraq, was an invited guest of Rep. Lynn Woolsey, D-California. Woolsey has called for a withdrawal of troops in Iraq and supports legislation for the creation of a Department of Peace.

Sheehan gained national attention in August when she and hundreds of other protesters camped outside Bush's ranch in Crawford, Texas, and demanded an audience with the president.

She also recently penned a book, "Not One More Mother's Child."

In April 2004, Sheehan and other relatives of troops killed in Iraq met with Bush during a visit to Fort Lewis, Washington, shortly after the death of her son, Army Spc. Casey Sheehan, 24.

Sheehan later said that the president wouldn't look at pictures of her son and "didn't even know Casey's name."

The Vacaville, California, resident has said she'd like to meet with Bush again to discuss her opposition to the war.

The president has declined another meeting and has taken issue with Sheehan's calls for a withdrawal of troops from Iraq.

"She expressed her opinion; I disagree with it," Bush said in August. "I think immediate withdrawal from Iraq would be a mistake."

CNN.com's Eliott C. McLaughlin contributed to this report.