A group of Democratic senators sent a letter to Google CEO Sundar Pichai calling for the company to convert its 120,000 temporary and contract workers into traditionally employed, full-time workers, The New York Times reported.

Ten senators signed the letter, including presidential candidates Kamala Harris, Bernie Sanders and Elizabeth Warren.

The letter sent last month also called for pay parity for temps, prohibiting conversion fees by staffing agencies, limiting the use of independent contractors and eliminating noncompete clauses.

“It is not enough to insist that contracting and staffing companies pay at least $15 an hour and provide healthcare and paid parental leave because that standard is well below that set for Google’s full-time employees,” according to the letter. “Google should convert contractors and temporary workers to full-time employees.”

The senators aren’t the first to challenge Google. Presidential candidate Pete Buttigieg released an economic plan last week that raised concerns about the company’s use of contingents.