Moving swiftly, the Secret Service forced out three agents Wednesday in a prostitution scandal that has embarrassed President Obama. A senior congressman welcomed the move to hold people responsible for the tawdry episode but warned "it's not over."

Along with three Secret Service employees leaving, eight other employees remain on administrative leave, the agency announced Tuesday evening.

One supervisor was allowed to retire, and another faces termination proceedings. The third, a non-supervisory employee, resigned, the agency said.

"These are the first steps," said Rep. Pete King, chairman of the House Homeland Security Committee, which oversees the Secret Service. King said the agency's director Mark Sullivan, took action against "the three people he believes the case was clearest against." But King warned: "It's certainly not over."

It is unclear if more firings are imminent, but one federal law enforcement official said the number of firings would be between two and "a handful."

The scandal was made public Saturday. As many as 11 agents and 10 military servicemembers allegedly brought prostitutes back to their hotel in Cartagena, Colombia, while doing advance work before the president's arrival for a trade summit.

The swelling scandal has raised questions about the "secret" culture at the nation's elite protection agency -- and few are feeling the heat more intensely than its director, Mark Sullivan.

Rep. Bennie Thompson, D-Miss., the top Democrat on the House Homeland Security Committee, said he’s had concerns about the Secret Service since two socialites crashed a White House state dinner in November 2009 and were allowed to get close to the president and vice president.

"Something like this is equally as troubling. At some point, (Sullivan) has to take responsibility," Thompson said.

But so far, officials on both sides of the aisle are largely defending Sullivan's leadership.

Even so, Reps. Darrell Issa, R-Calif., and Elijah Cummings, D-Md., the leading members of the House Oversight Committee, sent a letter to Sullivan urging him to take action.

In the letter, obtained by Fox News, Issa and Cummings tell Sullivan his “task is to restore the world’s confidence in the U.S. Secret Service.”

They then go on to ask 10 questions of Sullivan which they would like answered by May 1.

The questions include what is his understanding is of the agents' misconduct, what discipline is involved, a sense of whether there have been previous incidents and discipline, what agency failures may have led to the incident and how he will alleviate future problems.

In addition, the congressmen tell Sullivan that his “swift and decisive action” has “given us confidence” that future lapses won’t happen.

The Associated Press contributed to this report.