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A US senator and a pair of consumer privacy groups sent letters Tuesday to the Federal Trade Commission expressing concern over YouTube's practices surrounding kids content. They called on the agency to take action against the Google-owned video site for any wrongdoing.

Sen. Ed Markey, a Democrat from Massachusetts, urged the FTC to "hold YouTube accountable for any illegal activity affecting children that the company may have committed." This follows a June 19 report that YouTube is under investigation by the FTC for allegedly violating the Children's Online Privacy Protection Act.

COPPA passed in 1998 and includes guidelines prohibiting the collection of data on children under 13 without parental consent. Last year, a coalition of child advocacy, privacy and consumer groups filed a complaint with the FTC that alleges YouTube failed to get such consent.

"Personal information about a child can be leveraged to hook consumers for years to come," Markey wrote in the Tuesday letter. "It is incumbent upon the FTC to enforce federal law and act as a check against the ever-increasing appetite for children's data." Markey pointed out that YouTube channels directed toward kids have millions of subscribers.

Also on Tuesday, the Center for Digital Democracy and the Campaign for a Commercial-Free Childhood sent a letter to the FTC with a list of recommended penalties, including the deletion of user data on all children, civil penalties and "a $100 million fund to be used to support the production of noncommercial, high-quality and diverse content for children."

YouTube and Google were also scrutinized during a Senate subcommittee hearing on "persuasive technology." Sen. John Thune, a Republican from South Dakota, said companies like YouTube's parent Google, as well as Facebook, should offer consumers options that don't use algorithms to control what they see, according to Bloomberg.

Thune said the use of YouTube's algorithms to drive engagement could have an "unintended and possibly even dangerous downside."

Neither Google nor the FTC immediately responded to requests for comment.

CNET's Richard Nieva contributed to this report.

Originally published June 25, 2:15 p.m. PT.

Update, 4:27 p.m.: Adds comments from Sen. John Thune.