Sens. Lisa Murkowski, R-Alaska, and Ron Wyden, D-Ore., have unveiled a bipartisan campaign finance disclosure proposal, signaling a possible breakthrough for advocates of new political money restrictions.

Until now, not a single Senate Republican has come out in favor of legislation to shed more light on political spending. The leading Democratic disclosure bill, known as the Disclose Act, was blocked in the Senate in July by uniform GOP opposition.

The Murkowski-Wyden proposal, which the two senators unveiled on their websites and in an op-ed in The Washington Post, differs from the Disclose Act, but like that bill, would require unrestricted outside groups that spend money on campaigns to publicly report their funding sources. The two senators invited public comment by Jan. 15, and said they plan to introduce a bill early in the 113th Congress.

“Along with many Americans, we are uncomfortable with the Citizens United decision,” wrote Murkowski and Wyden in the Post, referring to the Supreme Court’s 2010 ruling to deregulate independent campaign spending. “Unlimited corporate and individual spending is corrosive to democracy and undermines the political process. But the case has been decided, and it is our prerogative as legislators to improve it. What we, and you, can do is shine a bright light on the system the court created to ensure accountability for all who attempt to influence the democratic process.”

The Murkowski-Wyden proposal would require any organization spending $500 or more on federal political activity, “from candidacy to advocacy,” as the two describe it, to disclose their donors in real time. The plan would also require the Internal Revenue Service and the Federal Election Commission to “establish joint regulations and guidance” on what constitutes election-related activity.

Senate Minority Leader Mitch McConnell, R-Ky., has already signaled his intent to stand firm against any attempts to tighten campaign finance rules. The Murkowski-Wyden plan is also certain to draw fire from advocacy groups that have opposed the Disclose Act on First Amendment grounds.