The news: Ten Democratic senators—including presidential hopefuls Kamala Harris, Bernie Sanders, and Elizabeth Warren—have asked Google to turn its army of temporary workers into full-time employees. The senators wrote in a letter to Google CEO Sundar Pichai that “the differences between the categories of workers appears to be in name only,” and so the company should “treat all Google workers equally.” They ask Google to, among other things, make temporary employees full-timers after six months, provide equal wages and benefits for all types of employees, and hire contractors only for work that isn’t already done by full-timers.

The build-up: Today’s letter follows a growing wave of concern over working conditions in the tech industry. It specifically cites a New York Times article about Google’s “shadow work force” of 121,000 temps that outnumber its 102,000 full-time workers (as of March). Other works on this theme include an investigation into the grueling conditions of Facebook content moderators and a recent book by anthropologist Mary L. Gray about “ghost workers,” or the underclass of contractors that power our technology. Amidst increasing talk of tech workers unionizing, Democratic presidential candidate Pete Buttigieg recently said that gig workers (many of whom work for technology companies like Uber) should be allowed to unionize.

What does Google say?: The senators gave Google until August 9 to respond, but the company is already pushing back. Google says that it does not mistreat contractors and that being a temporary worker is not supposed to be a path to a full-time job, according to a copy of a letter sent by a Google exec to the senators. Ultimately, today’s letter is unlikely to have a lot of immediate impact, but it’s the strongest evidence yet that Big Tech is coming under labor scrutiny from some of the most high-profile politicians in the country.