Jacinda Ardern says Simon Bridges is being "alarmist and dramatic" over law changes that may allow union representatives to enter workplaces without the consent of the business owner.

Mr Bridges raised the issue in Question Time today, stating the power given to union representatives appears to be greater than that of the police.

"Why will union representatives not be required to gain consent from an employer before entering the premises of their workplace when even a police officer has to ask a judge for a warrant?" Mr Bridges asked the Prime Minister.

Ms Ardern replied that it may not be the case that all union representatives will be allowed into a workplace without knowledge of the business owner.

"If there are health and safety regulations that require the representative to do so then they will have to ask permission," Ms Ardern said.

Deputy Prime Minister Winston Peters then stepped into the fray with a supplementary question for Mr Bridges.

"Using the members previous question, does a policeman in hot pursuit of a suspected murderer inside a office situation have to spend all the time for a warrant to go and pick that person up?" Mr Peters asked.

The reply from the National Party leader had even Mr Peters laughing.

"Can the Minister confirm that we are giving unions the same powers that we give to police officers when they are in hot pursuit of murderers?"