The Conservative Party says MP Lucy Allan has been suspended for backing a Reform UK candidate.
Ms Allan is standing down in Telford, Shropshire, and publicly gave her support to Reform's Alan Adams rather than Tory Hannah Campbell.
A Conservative Party spokesman said she had been suspended "with immediate effect", and that "a vote for Reform is a vote for Keir Starmer".
Ms Allan said she had resigned from the party to support Mr Adams to be the area's next MP.