It pays to have friends in high places.
Kanter, a Turkish citizen born in Switzerland, had his Turkish passport revoked two years ago over public criticism of President Recep Tayyip Erdogan.
Kanter skipped two road games outside of the United States last season - in Toronto against the Raptors as a member of the Portland Trail Blazers, and the NBA's London Game as a member of the New York Knicks.
"There's a chance I can get killed out there," Kanter said of traveling to Britain at the time.
"Setting aside our respect for Enes Kanter as a professional basketball player and athlete, we applaud Mr. Kanter's willingness to speak freely against authoritarianism, even as he and his family are threatened," the Democratic senators said in a joint statement Tuesday, according to the Boston Globe's Nicole Yang.
Kanter signed a two-year contract with the Celtics earlier this month. While the 2019-20 NBA schedule hasn't been released yet, Boston will play up to two regular-season games in Toronto. The Celtics aren't involved in any overseas contests this season.