Reps. Michele Bachmann (R-Minn.) and Marsha Blackburn (R-Tenn.) have withdrawn from their speaking slots at the National Tea Party Convention after controversy mounted about how proceeds would be used.

The convention is "for-profit," and the lawmakers worry that their participation might violate last week's Supreme Court decision in Citizens United vs. FEC. (For background on the ethics issue, see here.)

"Due to conflicting advice on whether Rep. Bachmann’s participation in the upcoming Tea Party Nation Convention would be in line with the Committee on Standards, Congresswoman Bachmann has decided not to participate in the event," said spokeswoman Debbee Keller.

She added:

There is uncertainty about how any proceeds from the event may be used, and we must err on the side of caution. Some will want to portray her withdrawal as a repudiation of the Tea Party Movement, but that couldn’t be further from the truth. Congresswoman Bachmann remains encouraged by all Americans, regardless of political party, who are concerned about this nation’s future and dwindling prosperity, and continues to be inspired their passion.

Blackburn also announced Thursday that she will withdraw from participation. The Tennessee Republican said she conveyed her doubts directly to the convention's organizer.

"I spoke to Judson Phillips this morning and let him know that I could not participate in the convention. I told him frankly that Tea Party Nation’s for-profit status has put many of his speakers in an awkward position," she said.

In a statement, her office said Blackburn's decision came after consultation with House ethics officers:

After consulting with the Committee on Standards, Congressman Blackburn has decided not to participate in the Tea Party Nation Convention next week. Standards advised Congressman Blackburn not to participate in the event due to uncertainty about how any proceeds from the event may be used. Convention organizers have not been clear about how those funds will be put to use. We have every indication that any profit could be put to work to advance grass roots causes and some of those uses could make the Congressman’s participation improper after the fact. 

A number of sponsors have also pulled out of the event after doubts were raised about whether organizers were trying to profit from the convention.

Sarah Palin is still slated to speak at the event, scheduled for Feb. 4-6 in Nashville.