(CN) - Minnesota Sen. Al Franken will make an announcement Thursday to address growing demands for him to resign due to multiple women accusing him of sexual misconduct.
Franken's support among his fellow Democrats collapsed dramatically on Wednesday after a former Democratic congressional aide told Politico he tried to forcibly kiss her after a taping of his radio show in 2006.
Franken vehemently denied the incident occurred, saying in a statement that the allegation was "categorically not true."
The woman, who was not identified, said Franken pursued her after her boss had left and she was collecting her belongings. She said she ducked to avoid his lips, and that Franken told her: "It's my right as an entertainer."
Franken, in his statement, said the idea he would claim such conduct as a right as an entertainer was "preposterous."
But the seantor's denial failed to hold off an avalanche of calls to resign on Capitol Hill.
Sens. Kirsten Gillibrand, D-N.Y., Patty Murray, D-Wash., Claire McCaskill, D-Mo., Mazie Hirono, D-Hawaii, Kamala Harris, D-Calif., and Maggie Hassan, D-N.H., all called on Franken to step down. Some Democratic men later joined them.
"I'm shocked and appalled by Sen. Franken's behavior," Murray 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. It's time for him to step aside."
Gillibrand said "it would be better for our country if he sent a clear message that any kind of mistreatment of women in our society isn't acceptable by stepping aside to let someone else serve."
With Franken's position appearing untenable, his office issued a statement saying, "Senator Franken will be making an announcement tomorrow. More details to come."
Franken already faced a Senate Ethics Committee investigation into previous claims by several other women that he groped them or sought to forcibly kiss them.
"This allegation is categorically not true and the idea that I would claim this as my right as an entertainer is preposterous," Franken said. "I look forward to fully cooperating with the ongoing ethics committee investigation."
The allegations against Franken began in mid-November when Los Angeles radio anchor Leeann Tweeden accused him of forcibly kissing her during a 2006 USO tour.
Several other allegations have followed, including a woman who says that Franken put his hand on her buttocks during a picture pose at the Minnesota State Fair in 2010. Two women, who asked to remain anonymous, have told the Huffington Post that Franken squeezed their buttocks at political events during his first campaign for the Senate in 2008. A fourth woman, an Army veteran, alleged Franken cupped her breast during a photo op on a USO tour in 2003.
Franken has apologized for his behavior but he has disputed some of the allegations.
The Associated Press contributed to this report.