Former Woolworths chairman John Dahlsen wants large-format retailers including hardware giant Bunnings to be subject to a mandatory code of conduct, warning suppliers and customers need better protection from monopoly players.

The boss of Dahlsens Building Centres and a former director of department store Myer and ANZ Banking Group, the corporate veteran said Australia was entering an era of mega-retailers, led by “industry crushers” and that a new code and industry ombudsman was needed to protect competition.