– Sen. Amy Klobuchar and a group of fellow U.S. senators are proposing stronger disclosure rules for paid political ads on sites like Facebook, Google and Twitter, in an effort to prevent covert foreign influence of American elections.

The legislation they unveiled Thursday follows revelations that Russian interests bought online ads during the 2016 presidential campaign, which are not subject to the same disclosure requirements of radio and TV ads. It’s a loophole that’s grown wider as more voters primarily get information online, and the senators said they would push to enact a law before the 2018 midterm elections.

“This exposes a national security vulnerability when it comes to online ads, a space where our laws have failed to keep up with technology,” Klobuchar said at a news conference. She is sponsoring the measure along with Sen. Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee; and Sen. John McCain, the Arizona Republican who chairs the Armed Services Committee.

Klobuchar, who cast the issue in terms of national security, added: “Our next election is 383 days away.”

The proposal follows the disclosure last month by Facebook that Russian operators spent $100,000 for political ads that were seen by an estimated 10 million citizens — even though foreigners are legally prohibited from spending money to influence a U.S. election. The Senate’s Intelligence and Judiciary committees, the latter of which counts Klobuchar as a member, are investigating Russian interference in the last presidential election.

Those investigations are separate from the inquiry by Special Counsel Robert Mueller, who can bring criminal charges if he uncovers criminal wrongdoing.

The Senate legislation would compel big tech companies to make reasonable efforts to ensure that the political ads on their sites aren’t tied to foreign actors. Facebook said last month that it would provide the contents of 3,000 ads bought by a Russian agency to congressional investigators and make political advertising on its platform more transparent.

CEO Mark Zuckerberg said his company will require political ads to disclose who is paying for them.

Warner and Klobuchar have said their bill would “formalize, and expand” on that promise. Tech executives are expected to testify during a congressional hearing on the proposal that’s scheduled for Nov. 1.

Klobuchar said it’s not yet clear whether online companies would support the measure. But, she said, “they have to realize that as the world has changed and they have been selling ads to people and making money … they have an obligation, just like TV and radio have, to disclose this to the public.”

Warner acknowledged that the legislation offered what he called a “light touch approach” that doesn’t address the problem of a foreign agent who is trying to conceal his identity. He said he wants social media companies to offer ideas to police the problem. His home state has a closely watched gubernatorial election next month.

“There will always be a place where things can fall through the cracks,” Warner said.

Sponsors acknowledge they would need to pass the bill by early next year to have an influence on the midterm elections — a tall order in a Congress that has struggled to come to an agreement on contentious issues.

It’s not yet clear if enough Republican lawmakers will get on board to elevate the measure’s prospects in the GOP-controlled Congress. Oklahoma Sen. James Lankford, a Republican on the Intelligence Committee, said he has some concerns about the bill including that “there is a difference between the public airwaves and privately held fiber, basically, and how it’s managed.”

Klobuchar floated the possibility of attaching the measure to a bigger piece of legislation, possibly the national security bill.

“I wonder who’s carrying the national security bill … Senator McCain!” she said.