A group of Democratic senators has demanded in a letter sent to Google’s chief executive, Sundar Pichai, that the internet giant convert its more than 120,000 temporary and contract workers to full-time employees.

The letter, written by Senator Sherrod Brown of Ohio, also urged Google to stop its “anti-worker practices” and treat everyone at the company equally.

“Making these changes to your company’s employment practices will ensure equal treatment of all Google workers and put an end to the two-tier employment structure you have perpetuated,” Mr. Brown wrote. Among the 10 senators who signed were three running for president: Kamala Harris, Bernie Sanders and Elizabeth Warren.

As of March, Google had more temporary workers than full-time employees — 121,000 temps and contractors and 102,000 full-timers, according to company data viewed by The New York Times.