A federal watchdog group filed a brief Tuesday opposing former Sen. Norm Coleman's (R-Minn.) bid to use his Senate campaign's funds to defend against a lawsuit in which his ethics are challenged.

Coleman has asked the Federal Election Commission (FEC) for permission to use campaign funds to prepare for potential depositions for lawsuits in which a Coleman donor is accused of funnelling money to the former Senator.

Citizens for Responsibility and Ethics in Washington (CREW) filed a brief Wednesday opposing Coleman's request, arguing that it would blue the line between personal and campaign expenses.

"Campaign funds should be used for campaign purposes and not for every legal expense a candidate incurs," CREW Director Melanie Sloan said in a statement.

"The FEC has expanded the exceptions to the ban on using campaign funds for personal use so much that they swallow the rule," Sloan added. "This is a good time for the Commission to cut back."

The suit, filed days before the 2008 election, may have swung enough voters against Coleman to have led to his likely defeat to Democrat Al Franken in a razor-thin race.