Dyson Heydon will announce whether he will resign from the royal commission into trade unions on Friday.

The commission has issued a statement saying Mr Heydon will announce his decision at 10am on Friday, and publish his reasons online "as soon as possible thereafter."

The commissioner – who has been accused of creating the apprehension of bias - was scheduled to deliver his decision on Tuesday, but on Monday afternoon delayed this without issuing a new timeframe.

Lawyers for unions that have appeared before the commission argued last week that the former High Court judge should disqualify himself following revelations he had agreed to speak at a Liberal Party fundraiser.