The European Commission is investigating porn platforms Pornhub, Stripchat, XNXX and XVideos over lapses in minor protection, the EU executive said Tuesday.

The investigations will center around the platforms’ age verification measures to keep minors away from adult content, as well as looking into how the platforms assess and mitigate risks related to children’s rights and users’ well-being.

The EU executive is concerned that the current system of self-declaration is not effective, a Commission official told journalists during a briefing Thursday morning. Information requested from the platforms shows that “they really [don’t have] an effective age verification system in place,” the official said.

Violation of the bloc’s digital content rules, the Digital Services Act, can result in a fine of up to 6 percent of the company’s annual global turnover. There is no time limit under which a probe must conclude.

The probes come as the issue of online protection of minors reaches the top of the EU agenda, both for member countries and the Commission, and may increase in scope.

“We are not excluding future expansion of the proceedings” into other issues under the DSA, such as illegal content or ad repositories, a second Commission official said.

In parallel, national authorities will work together to oversee smaller pornographic platforms’ compliance with the bloc’s digital rules under the Digital Services Board, the Commission said. The local authorities can open investigations, work together and “really kind of put pressure” on these smaller platforms, said the first Commission official.

The Commission also rescinded the designation of Stripchat as a very large online platform, after the platform reported user numbers under the 45 million threshold. VLOPs, which include Pornhub, XVideos and XNXX, have to follow stricter rules under the DSA.

Pornhub, Stripchat’s owner Technius Ltd. and XNXX did not immediately respond to POLITICO’s request for comment. XVideos told POLITICO that it was not aware of the investigation so it couldn’t comment.