Ashurst's underpayments of well-paid graduate lawyers is a warning to law firms that have long put their heads in the sand on the issue of overwork.

The industry's reputation of gruelling work hours has often been dismissed as par for the course in a profession that attracts alpha employees and where workers are expected to make sacrifices before attaining the greater glories of partner.

But the revelation that staff on $80,000 a year could still earn less than a Coles shelf-stacker on a per hour basis upturns the sheen and glamour the industry has relied on to paper over the problem.

It also marks the spread of underpayment issues that have dominated retail and hospitality jobs to prestigious white-collar professions, where it has often been assumed underpayments cannot happen.

The point is underscored by the fact that Ashurst's underpayments are the result of the exact same issue that it advised Woolworths on – excessive unpaid hours of salaried staff – and which saw up to $300 million in underpayments at that company.

Now two-thirds of the big six law firms have confirmed they are reviewing their graduate lawyers' pay and hours for underpayments.