Democratic lawmakers on Wednesday urged the US Federal Trade Commission to investigate Google for marketing apps on its Play Store that allegedly violate a federal child privacy law.

In a by Sen. Ed Markey of Massachusetts and Rep. Kathy Castor of Florida, the lawmakers take aim at a Google program called Designed for Families, which pushes apps that the company says are compliant with the Children’s Online Privacy Protection Act. The law, also known as COPPA, regulates user data collection from sites with users who are under 13 years old. 

But the lawmakers from last month by child advocacy nonprofits that examined more than 150 apps that are part of the program and found that almost half of them share user data with outside parties. 

“The FTC must use its full authority to protect the interests of children, many of whom are increasingly online during the ,” the letter says. “Therefore, we urge you to investigate whether the Google Play Store has engaged in unfair and deceptive practices that mislead parents and harm kids.”

Google didn’t immediately respond to a request for comment. 

The letter comes as big tech companies are increasingly under fire in regard to child safety on their platforms. At a with the CEOs of Facebook, Google and Twitter, the tech leaders were slammed by both Democrats and kodekodean Republicans who accused the companies of exploiting kids to make money. 

Google has received blowback in the past for its treatment of children on its services. Two years ago, the FTC , as well as new requirements, for Google-owned YouTube’s violation of COPPA. In response, the video site made major changes to how it treats videos for kids, including limiting the data it collects from those views. 

YouTube Kids, a version of the video service specifically meant for children, faced controversy in 2017 when the service’s filters failed to recognize some videos that , like Mickey Mouse lying in a pool of blood, or PAW Patrol characters bursting into flames after a car crash. 

The letter follows another push by Castor for child safety from Silicon Valley companies. In September, she introduced the , in the House. The bill bans “auto-play” sessions on websites and apps geared for children and young teens. The legislation also bans push alerts targeting children and prohibits platforms from recommending or amplifying certain content involving sexual, violent or other adult material, including gambling or “other dangerous, abusive, exploitative, or wholly commercial content.”