Sundar Pichai, CEO of Google, speaks to the media before the opening of the Berlin representation of Google Germany in Berlin on January 22, 2019.

Ten U.S. senators are calling on Google to take "immediate action" to convert its growing number of contractors to full-time employees after six months of work.

The demand follows a New York Times report in May that said Google employed 121,000 contract employees and 102,000 full-time employees.

"Temporary workers and independent contractors are by definition intended for short-term and non-core work, and we urge Google to end any abuse of these worker classifications and treat all Google workers equally," the letter, which was addressed to Google CEO Sundar Pichai said. It asks for a response by Friday.

According to a Recode report in May, contractors made significantly less than full-time Google employees. Statistics from GlassDoor showed the median pay for contractors was $90,000 per year, while median pay for full-time employees was $128,000.

"The differences between the categories of workers appears to be in name only," the letter says. "In at least some cases, your company determines where these individuals work, the hours they work, the tasks they perform, and whether or not they should continue to work on Google contracts. In the case of temporary workers, they are commonly working on permanent projects alongside full-time Google employees for years and typically at much lower pay than their full-time employee counterparts."

The letter says these are "abuses" of classifications for contractors and temp workers. It's signed by Democratic Sens. Sherrod Brown, Patty Murray, Benjamin Cardin, Brian Schatz, Elizabeth Warren, Kamala Harris, Edward Markey, Richard Blumenthal, Richard Durbin and Bernie Sanders, who is an independent but caucuses with the Democrats.

"Google is valued at more than $100 billion, and your personal compensation topped $400 million in 2018, which makes it that much more difficult to stomach the mistreatment of these workers," the letter to Pichai said. "It is not enough to insist that contracting and staffing companies pay at least $15 an hour and provide health care and paid parental leave because that standard is well below that set for Google's full-time employees. Google should convert contractors and temporary workers to full-time employees."

The letter from the senators asks for the following immediate changes: