Three U.S. Democratic lawmakers on Friday urged the Federal Trade Commision (FTC) to ensure technology companies like Facebook, Alphabet's YouTube and TikTok comply with policy changes aimed protecting young people online.

The letter from Senator Ed Markey and Representatives Kathy Castor and Lori Trahan cited recent commitments by the companies amid growing concern by lawmakers about young people online. The FTC, said the letter seen by Reuters, has an "obligation to ensure that powerful technology platforms comply with their public statements and policies on children’s and teen’s privacy."

The FTC and Facebook declined to comment. TikTok and YouTube did not immediately comment.

Facebook came under harsh criticism from senators this week at a Senate Commerce subcommittee after hearing testimony from former Facebook employee Frances Haugen, who said she believes that "Facebook's products harm children, stoke division and weaken our democracy."

The lawmakers cited young people's increasing online use -- saying it was now on average almost five hours each day. "We therefore encourage you to use every tool at your disposal to vigilantly scrutinize companies’ data practices and ensure that they abide by their public commitments," they wrote.

Some changes have been prompted by a new UK law that took effect last month called the Age Appropriate Design Code. The lawmakers noted photo-sharing app Instagram publicly announced it is "defaulting young people into private accounts, making it harder for potentially suspicious accounts to find young people."

Last month, Instagram said it was pausing plans to develop a new app it is creating for kids.

The subcommittee chaired by Senator Richard Blumenthal is planning another hearing for as early as the week of Oct. 18 that is expected to include other major tech companies like TikTok, Snap and YouTube.

A committee spokesman said the hearing had not been finalized but the panel has secured commitments from several social media companies to appear in the coming weeks.