In a statement, the Secret Service said the three had chosen to resign. Six employees have left the agency following the April 11 incident, in which agents brought prostitutes to a hotel in Cartagena, Colombia, two days before President Barack Obama arrived for the Summit of the Americas.
Two of those who have lost their jobs have been identified as supervisors David Randall Chaney and Greg Stokes. Chaney has retired but Stokes faces termination for cause and could contest the matter, The Washington Post reported.
One of the agents initially investigated has been cleared of "serious misconduct" but may yet face administrative action the newspaper said.
The U.S. military said Friday 11 service members are suspected of participating in the episode.
The Secret Service departures come as the investigation expanded to determine whether the alleged misconduct was confined to the 11 employees first tied to the scandal, a senior U.S. official told The New York Times.
"We have no reason to believe anything else happened, but we want to have a complete and thorough investigation to ensure this didn't go any further," the unidentified official said.
The widening inquiry includes a review of agents and other personnel who had rooms at the Hilton Cartagena, where Obama and Secretary of State Hillary Clinton stayed, as well as the Hotel Caribe, where the 11 agents and 10 military officers implicated in the scandal had rooms.
The Secret Service and the Pentagon are conducting parallel investigations, including interviews with women believed to be prostitutes brought into Hotel Caribe.
Stokes, an assistant special agent in charge of the canine division, has the option to appeal his firing within 30 days, CBS News reported.
Chaney, a supervisor in the service's international programs division, has posted several on-duty shots of himself on Facebook, The Washington Post said, including one showing him behind former Republican vice presidential nominee Sarah Palin during her 2008 campaign.
"I was really checking her out, if you know what i mean?" Chaney wrote in the comments section, after friends admired the photo. He is 48, married and has an adult son.
The Facebook page appeared to be no longer public when United Press International tried to confirm the comments Thursday night but the images have been posted on other Web sites.
Neither Chaney nor Stokes had any immediate comment about the scandal, which came to light after an early-morning payment dispute between an agent and a woman he had brought to his hotel room.