US Republican Senator Josh Hawley being labelled transphobic on the floor of the Senate looked almost like it was "planned," former Republican US Senate nominee Rik Mehta says.

During congressional hearings on Tuesday, Senator Hawley questioned Berkeley law professor Khiara Bridges on whether the phrase “people with the capacity for pregnancy” referred to women.

Prof Bridges proceeded to denounce Mr Hawley's line of questioning as "transphobic" and said by denying that men have the ability to fall pregnant is akin to denying the existence of trans people.

"It's almost like it was pretext, it was canned and it was planned that she was going to come out and somehow get out that she was going to call Senator Hawley transphobic regardless of what he asked or said," Mr Mehta said.