U.S. Secret Service officials told lawmakers Thursday they are arranging polygraph and drug tests for employees implicated in an alleged prostitution scandal, and additional ousters are expected in coming days.

Secret Service Director Mark Sullivan took action against three of 11 men whom he pulled from duty in Cartagena, Colombia, last week after allegations that the men may have brought back prostitutes to their hotel. One supervisor resigned and another retired, and the agency said it would seek...