There may be a whole lot less dark money in federal elections after the Supreme Court allowed a lower court decision to go into effect on Tuesday invalidating a key regulation that created a loophole for undisclosed spending.

The decision came about after Citizens for Responsibility and Ethics in Washington, a liberal watchdog group, fought for the past six years to get the Federal Election Commission to enforce campaign finance laws against Crossroads GPS, a conservative nonprofit group founded by Karl Rove, a senior adviser to George W. Bush when he was president. CREW finally won its battle on Tuesday.

As of Sept. 18, any group that runs an independent expenditure election ads that expressly call for the election or defeat of a candidate in excess of $250 will have to disclose all political donors above $200.

This is a great day for transparency and democracy, Noah Bookbinder, CREWs executive director, said in a statement. Three courts, including the Supreme Court, have now rejected Crossroads arguments for a stay, meaning were about to know a lot more about who is funding our elections.