Rice is alleged to have assaulted Janay Palmer, his-since married fiance, in a Feb. 15 altercation in a casino elevator.
The NFL suspended Rice for two games, a shorter duration than some other players have received for violating the league's substance abuse policy.
“Mr. Rice’s suspension reflects a disturbingly lenient, even cavalier attitude towards violence against women,” the senators wrote.
The letter also calls for the league to "develop procedures to ensure that allegations and evidence of domestic violence are addressed appropriately."
The senators sent a separate, shorter letter to Ravens general manager Ozzie Newsome.
The three senators who co-signed the letters were Richard Blumenthal (D-Conn.), Tammy Baldwin (D-Wisc.) and Chris Murphy (D-Conn.).
At a news conference on Thursday, Rice addressed the media for the first time since being issued the suspension. "Violence of any kind, especially man on woman, is not right," Rice said. "I have to pay for that."
- Chris Johnson