The appearance of former NSW Premier Mike Baird before a parliamentary inquiry investigating the relocation of the Powerhouse Museum has been postponed until May 28.

Mr Baird's one time chief of staff, now Mirvac executive Bay Warburton, will give evidence to the Powerhouse inquiry three days later on June 1.

The former Premier Mike Baird is to make a delayed appearance before Powerhouse Museum inquiry. Credit:Brianne Makin

Both men are appearing voluntarily before the Powerhouse Inquiry following threats by the committee to invoke the Parliamentary Evidence Act, by which a Supreme Court judge can issue arrest warrants. There are also penalties for refusing to answer questions or giving false evidence.

But the evidence of both men, key figures in the government's decision to shift the museum to Parramatta before completion of a fully costed business plan, are likely to post-date a public announcement on the museum's fate.