LA radio host Leeann Tweeden was the first to come forward, alleging the congressman aggressively kissed her when the two were rehearsing for a skit while on a USO tour in 2006 and groping her while she was sleeping.
The aide, whose name POLITICO is withholding to protect her identity, said Franken (D-Minn.) pursued her after her boss had left the studio.
When she fled the room, Franken told her, "It's my right as an entertainer".
Franken has been accused of groping or trying to forcibly kiss six other women.
"Enough is enough. The women who have come forward are fearless and I believe them". "I was really startled by it and I just sort of booked it towards the door and he said, 'It's my right as an entertainer'".
Mr Franken, a former Saturday Night Live comedian, has been accused of groping and sexually harassing seven women, including a USA military veteran.
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She was joined by Mazie Hirono of Hawaii, Claire McCaskill of Missouri, Patty Murray of Washington, Kamala Harris of California and Maggie Hassan of New Hampshire, who issued statements in a coordinated effort that is likely to jeopardize Mr. Franken's political future.
The Democratic senator is among a growing list of politicians, entertainers and news media figures facing a wide range of allegations involving sexual misdeeds. Franken has apologized for most of the incidents and has said he would cooperate with a Senate ethics probe into his behavior.
If Franken were forced to resign, it wouldn't change anything immediately in the Senate, because there is a Democratic Governor in Minnesota, who would appoint a replacement, before a special election in that state.
"This allegation is categorically not true and the idea that I would claim this as my right as an entertainer is preposterous", he said. "It's clear to me that this has been a deeply harmful, persistent problem and a clear pattern over a long period of time".