Call it the Embarrass Rick Davis Act of 2008.

Rick Davis, of course, is John McCain's campaign manager, and has taken a hit for doing business with companies with ties to Iran. Now Barack Obama has signed on as a co-sponsor of a bill to subject American lobbyists like Davis to tighter disclosure requirements if they work on behalf of foreign entities.

During a conference call with reporters, Sen. Chuck Schumer insisted the bill wasn't primarily influenced by Davis, but instead by some lobbying activities by the Iraqi government that were discovered in recent weeks. However, he said, Davis would be affected by the bill.

Schumer invited McCain to sign on as a co-sponsor of the bill -- a pretty aggressive throwing down of the gauntlet, since it puts McCain in the tough spot of either signing on, and making life difficult for all the lobbyists on his campaign, or refusing, and ceding the reformer high ground to Obama.

No comment yet from the McCain camp.