We've asked Nelson's team if the fundraiser, to be held at Alex Sink's home near Tampa, is still on.
UPDATE: "Sexual harassment is never acceptable. The Senate Ethics committee will fully investigate this troubling incident, as I believe they should," Nelson said in a statement.
"As for the events this weekend, Sen. Franken is no longer available. The campaign events will continue as scheduled."
A radio host, Leann Tweeden, said Franken made unwanted advances while practicing a skit for a USO tour in 2006.
"I certainly don't remember the rehearsal for the skit in the same way, but I send my sincerest apologies to Leeann," Franken said in a statement. "As to the photo, it was clearly intended to be funny but wasn't. I shouldn't have done it."
Franken, through his PAC, gave $10,000 to Nelson's 2012 campaign and another $10,000 for the upcoming run.
Republicans have demanded he return the money. Nelson hasn't yet said what he'll do.
UPDATE 2: Nelson will donate the money to charity, a spokesman said.
Note: The headline of this post was updated to reflect that Franken will no longer appear at the fundraiser.