Treasurer Jim Chalmers insists his changes to the Future Fund’s investment mandate are legal, but the sovereign wealth fund’s first chairman, David Murray, says the government’s new directive appears to breach the law.

Future Fund chairman Greg Combet and Dr Chalmers on Friday refused to release legal advice underpinning their assessment that the new mandate requiring the $230 billion fund to prioritise investments in housing, energy and infrastructure did not contravene the law preventing the government from directing the fund where to put its money.