The Trump administration pressed its offensive against online companies it accuses of censoring conservatives, asking regulators to dilute a decades-old law that social media giants such as Facebook Inc., Twitter Inc. and Google say is crucial to them.

The Commerce Department on Monday asked the Federal Communications Commission to write a regulation weakening protections laid out in Section 230, language in a 1996 law that protects online companies from legal liability for users’ posts, and for decisions to remove material.

“Social media and its growing dominance present troubling questions on how to preserve First Amendment ideals and promote diversity of voices in modern communications technology,” the National Telecommunications and Information Administration, a Commerce Department arm, said in its petition to the FCC.

The request renews attention on web companies ahead of an antitrust hearing in Congress on July 29 that is to feature chief executives of Inc., Facebook, Google parent Alphabet Inc. and Apple Inc. The hearing concerns competition online, and it may also include discussion of web posting practices. Facebook, for example, has faced accusations it doesn’t adequately police hateful and misleading content. The company says it has increased efforts to fight misinformation and stymie election interference.

Monday’s action by the Commerce Department fulfills part of an executive order that President Donald Trump signed in May after Twitter labeled several of his posts as potentially misleading. Trump cited Twitter, Google, Facebook “and perhaps others” and said online companies have “unchecked power to censor, restrict, edit, shape, hide” communications.

Times have changed since the law giving the platforms liability protection was written, and “a handful of large social media platforms” have replaced a “sprawling world” of dial-up internet service providers and countless bulletin boards, according to the NTIA petition.

FCC Chairman Ajit Pai earlier said the agency would “closely review” a request from the Commerce Department.

The executive order is the latest in a years-long campaign by the president and his allies against social media companies. The companies say they’re combating disinformation and foreign interference after the federal government found that Russia used U.S. social media to try to influence the 2016 election.

Online companies have protections against lawsuits when they act “in good faith” in suppressing social media posts, but the law doesn’t define bad faith. According to Trump’s executive order, the FCC would issue rules clarifying the issue. This could allow users to sue over takedowns.

In June, the Justice Department asked Congress for a broad overhaul of legal protections for online platforms if they deliberately promote illegal speech on their websites. The proposals could upend the companies’ business models, and also limit their discretion to remove political posts.

The Internet Association, a trade group representing major online providers, has sought to refute accusations of unfairness. “Claims of so-called viewpoint bias rely on isolated anecdotes,” Interim President and Chief Executive Officer Jon Berroya said in a May 28 statement. The group said the Justice Department’s proposed changes would bring a threat of litigation to content moderation decisions, making it harder to ensure sites are safe.