Several groups of American Secret Service employees visited clubs, bars and brothels in Colombia and engaged in "morally repugnant" behaviour before a visit by President Barack Obama, a US senator has said.
Susan Collins said the agents' actions in the prostitution scandal could have provided a foreign intelligence service, drug cartels or other criminals with opportunities for blackmail that could have threatened the president's safety.
In remarks prepared for the first congressional hearing on the matter today, Ms Collins also challenged early assurances that the scandal in Colombia appeared to be an isolated incident.
The senator from Maine noted that two participants were secret service supervisors - one with 21 years of service and the other with 22 years - and both were married.
Their involvement "surely sends a message to the rank and file that this kind of activity is tolerated on the road", Ms Collins, the senior Republican on the Senate homeland security and governmental affairs committee, said.
"This was not a one-time event. The circumstances unfortunately suggest an issue of culture."
Today's hearing is expected to expose sensational new details in the scandal, which became public after a dispute over payment between a secret service agent and a prostitute at a Cartagena hotel on April 12.
The secret service was in the coastal resort before Mr Obama's arrival for a Latin American summit.
Ms Collins said several small groups of agency employees from two hotels went out separately to clubs, bars and brothels and they "all ended up in similar circumstances".
"Contrary to the conventional story line, this was not simply a single, organised group that went out for a night on the town together," Ms Collins said.
Senators were expected to focus on whether the secret service permitted a culture in which such behaviour was tolerated.
US homeland security secretary Janet Napolitano has testified previously that she would be surprised if there were other examples, but senators have been sceptical.
In his own prepared remarks, secret service director Mark Sullivan told senators the behaviour in Colombia was not representative of the agency's 7,000 employees.
Mr Sullivan assured senators that Mr Obama's security was never at risk.
The officers implicated in the prostitution scandal could not have inadvertently disclosed sensitive security details because their confidential briefing about Mr Obama's trip had not taken place.
A dozen secret service officers and supervisors and 12 other US military personnel were implicated.
Eight secret service employees, including the two supervisors, have lost their jobs.
The secret service is moving to permanently revoke the security clearance for one other employee, and three others have been cleared of serious wrongdoing.
Four of the secret service employees have decided to fight their dismissals.
Prostitution is legal in Colombia, but Mr Sullivan quickly issued new guidelines making clear that agents on assignment overseas are subject to US laws.