The Public Service Association says a threat to lock out Parliamentary security officers is unacceptable bullying.
About 80 union members at Parliament, including security guards, were on strike for two hours on Thursday over pay issues.
The strike coincided with Question Time in Parliament, but did not disrupt proceedings.
The Parliamentary Service says the action left the precinct insecure and it will lock out security staff if it happens again.
The PSA says the threat is heavy-handed.
National secretary Richard Wagstaff says preventing security officers from doing their job for an indefinite period would pose a far greater risk to Parliament's security than them taking lawful protest action.