The lawyers signing the request — Marc E. Elias, Ezra W. Reese, Jonathan S. Berkon and Rachel L. Jacobs — work at Perkins Coie, the marquee Democratic election firm, which also represents the party’s congressional campaign committees, the presidential campaign of Mrs. Clinton and a Democratic super PAC supporting her. Mr. Elias declined to comment beyond the filing.

The brief, filed on behalf of two Democratic super PACs with ties to the party’s congressional leadership, Senate Majority PAC and House Majority PAC, could signal a turning point in the churning legal war between proponents and opponents of tighter campaign regulation.

The six-member Federal Election Commission — which by law can have no more than three commissioners from one party — has not yet acted on an array of legal challenges and complaints filed by watchdog groups in recent months over the activities of presidential campaigns and their super PACs. And while independent groups are an ever-growing portion of election spending, the commission has been unable to come to an agreement on comprehensive new rules for the groups, which arose after the Supreme Court’s Citizens United decision in 2010.

Democrats have generally called for tighter restrictions on super PACs, seeking new rules legislatively and even going to court to force the commission to act. But the new request takes a very different tack: In effect, the lawyers are arguing, the commission’s inaction threatens to put Democrats at a competitive disadvantage.