Sen. Al Franken is calling for the Federal Election Commission to investigate allegations from a liberal group that the U.S. Chamber of Commerce —  the pro-business association that’s said it will spend $75 million on the midterm elections — used money from foreign corporations for its political ads.

The Chamber denies the allegations.

The charges were made Tuesday by Think Progress, a blog run by the progressive Center for American Progress Action Fund.

Essentially, Think Progress claims the Chamber’s foreign chapters, which collect dues from foreign corporations, send that money directly to the Chamber’s main headquarters in Washington, which in turn uses the foreign funds for its political spending.

Franken’s letter says that the Chamber’s mixing of funds under current FEC rules “is not per se illegal.” But he wrote that the company had to demonstrate that its foreign funds were not used for political purposes, and pushed the FEC to launch an investigation.

In addition, Franken’s letter asked the FEC to change its regulations allowing foreign companies to spend on elections — which is legal so long as the company is incorporated in the U.S. and creates a special election committee staffed by Americans.

Franken has been a leading proponent in Congress of the Disclose Act, which would require greater disclosure of funding sources for independent groups running political advertisements. Franken, a co-sponsor of the bill, authored the provision that would prevent foreign-owned companies from spending on U.S. elections.

The bill, proposed in the wake of the Citizens United Supreme Court decision that rolled back corporate election spending laws, failed last month to break a filibuster in the Senate 59-39. Franken told Hot Dish he doesn’t think it will pass in the current Congress.

Read the letter below:

Franken FEC Letter