JEFFERSON CITY, Mo. -- The Missouri Republican Party has filed a complaint with the U.S. Senate ethics committee over Democratic Sen. Claire McCaskill's use of a private airplane.

The complaint publicized Tuesday by Republicans comes after McCaskill repaid the U.S. Treasury $88,000 last week for 89 airplane trips she organized through a company in which she and her husband have an ownership stake. Senate rules allow lawmakers to be reimbursed for travel, but McCaskill said she repaid the money to avoid the appearance of a conflict of interest.

Politico.com subsequently reported that one of those trips was for political purposes -- when McCaskill traveled from St. Louis to Hannibal for a Democratic conference in March 2007.

McCaskill spokeswoman Maria Speiser said Tuesday the political trip was mistakenly billed to the government.

She said McCaskill was embarrassed by the incident.