This week, a bipartisan group of US senators took the first steps toward regulating online political advertising in a manner similar to the way the government already regulates these ads in traditional media. Democratic Sens. Amy Klobuchar (MN) and Mark Warner (VA), joined by Republican Sen. John McCain (AZ), say their Honest Ads Act will protect against foreign interference in elections by requiring platforms like Facebook to make details about ads’ buyers, pricing, and targeting publicly available.

Advocates cheered the move, which they said represented a long-overdue step to apply the same standards of transparency and fairness to online ads that have long been the norm for print, radio, and television. At the same time, the bill’s passage is far from certain: so far, it has just one Republican supporter in Congress, and the tech companies that would be affected have deployed a phalanx of lobbyists.

“It goes a long way,” said Alex Howard, deputy director of the Sunlight Foundation, which advocates for transparency in political advertising and helped to draft the legislation. “Opacity by design is not an acceptable status quo for the technology giants that shape public knowledge and discourse with limited accountability,” he wrote in a blog post after the bill’s introduction. “We’re excited to see bipartisan support for more transparency and accountability online.”

The Honest Ads Act would require large platform companies like Facebook and Google to retain copies of the political ads they serve and make them available for public inspection. The companies would also have to publish information about who bought the ad, how much it cost, and what rates they were charged. The act would apply to any platform with more than 50 million monthly users, and anyone who spent more than $500 a year on online ads.

“It goes a long way.”

Publicly, tech companies are voicing support for some form of regulation — while stopping short of offering a full-throated endorsement of the Honest Ads bill’s actual provisions. “We stand with lawmakers in their effort to achieve transparency in political advertising,” said Erin Egan, vice president of US public policy for Facebook, in a statement. “We have already announced the steps Facebook will take on our own and we look forward to continuing the conversation with lawmakers as we work toward a legislative solution.”

Facebook has already committed to making copies of ads publicly available. It also pledged to make more prominent disclosures about who paid for the ads on the advertisements themselves. It’s part of the company’s nine-point plan to reset Facebook’s relationship with democracy, which CEO Mark Zuckerberg laid out last month after mounting pressure to act.

But while the company isn’t commenting beyond Egan’s statement, it’s likely Facebook would oppose several provisions within the act. For one thing, the company has a long history of opposing regulation of its ads. For another, the requirement to disclose the pricing for every political ad goes beyond what is required for print and broadcast ads. (The the equal-time rule does require radio and television stations to offer equivalent time to political candidates if they ask for it, and at the same price, though those prices are not generally accessible to the public.)

The requirement to post targeting information could meet resistance as well. Until now, politicians have been able to target different groups of voters in stealth, using so-called “dark posts,” which appear only in the News Feed and don’t have permanent links. Forcing candidates to admit they’re targeting different messages at voters — especially inconsistent ones — could have a chilling effect on their use of Facebook’s ad platform.

But the bill’s sponsors say such disclosures are essential to protect against foreign interference in US elections. “Who wouldn't want to know if the ad that's appearing next to your story was actually paid for by a foreign power?” Warner said yesterday. “I don't know what opposition there would be to that kind of disclosure.” (It’s actually illegal for foreigners to buy election ads.)

Now the question is how much momentum the bill can generate. In addition to the Sunlight Foundation, it received endorsements from advocacy groups, including the Campaign Legal Center, Issue One, the Brennan Center of Justice, Common Cause and Public Citizen. And The Washington Post reported that a companion bill was introduced in the House Thursday by Reps. Derek Kilmer, a Washington Democrat, and Mike Coffman, a Colorado Republican.

“It’s the wild wild west.”

Sen. Lindsey Graham, a South Carolina Republican told the Post he is “very interested” in the Honest Ads Act. “Social media advertising had to be regulated, it’s the wild wild west,” said Graham, a longtime McCain ally. “When it comes to disclosing who pays for online advertisements, he continued, “You’ve got to try to apply the same rules you would to radio and TV.”

For Klobuchar and Warner, that represents a good start. But the real battle is only beginning. And with lobbyists ramping up their involvement, much of the fight over transparency in advertising will play out behind closed doors.