Intimidation 101.

(Reuters) – Democratic President Barack Obama’s top campaign lawyer filed a complaint with the federal election regulator on Tuesday, demanding that the well-heeded and high-spending Republican advocacy group Crossroads GPS disclose its donors.

This is the latest Democratic effort to slow down Crossroads GPS, run by former aide to President George W. Bush Karl Rove, which plans to spend some $300 million alongside its sister “super” political action committee to help Republican candidates ahead of the November 6 election, largely through advertising.

Republican non-profit and “Super PAC” groups have been far outpaced their Democratic rivals in fundraising and spending, which expected to help presumed Republican presidential nominee Mitt Romney bridge the fundraising gap between his and Obama’s election campaigns.

Crossroads GPS is organized under a specific U.S. tax law section that identifies it as a nonprofit social welfare organization, meant to educate the public and allowed to keep its donors private. The group also has a sister Super PAC American Crossroads, which discloses its donors monthly.

The Federal Election Commission, the elections oversight agency, is currently split along party lines and has repeatedly deadlocked on whether social welfare groups must disclose their donors if they engage in political activity.