The head of the Oklahoma Republican Party is under pressure to either withdraw her endorsement in a Congressional race or resign.

Four former leaders of the state GOP say the current chair, Charity Linch, inappropriately used her position to endorse Jackson Lahmeyer in the race for the open seat in Oklahoma’s First Congressional District. Nathan Dahm, A.J. Ferate, Pam Pollard and Gary Jones wrote in a statement that the state GOP has a decadeslong custom for sitting chairs to stay out of primary elections for open seats to let voters pick the nominee.

Eleven Republicans are seeking the open Tulsa area seat.