The Engineering, Printing and Manufacturing Union says it suspended a senior worker for failing to seek permission to run as an ACT Party candidate in this year's election.
Shawn Tan is a negotiator for the union and was earlier this week announced as number 10 on ACT's party list.
The union's national secretary Andrew Little says running as a candidate bears upon a worker's employment because it is time-consuming.
He says Mr Tan knew he had to apply for permission following discussions with the union earlier this year.
Mr Little says if Mr Tan had sought permission, the union would have to consider that ACT's policies are contrary to the interests of the union's members.
ACT has accused the EPMU of over-reacting. Its leader Rodney Hide says Mr Tan feels aggrieved about being suspended because he hadn't tried to push his beliefs through the EPMU.