The Fair Work Ombudsman has said Qantas is paying back millions of dollars to hundreds of workers it underpaid for up to eight years.

The airline had so far paid back $7.1m to 638 staff at head office who were underpaid between June 2011 and June 2019, the ombudsman said on Friday.

The airline self-reported it had incorrectly paid some marketing and administrative staff in accordance with their individual contracts, rather than their relevant enterprise agreements that covered them, the ombudsman, Sandra Parker, said.

As a result, they didn’t receive the minimum terms of those agreements, such as overtime, minimum wages and annual leave entitlements, she said.

Under a court-enforceable undertaking, Qantas has agreed to repay all workers, with interest, and give each affected worker an additional $1,000 payment by 24 April.

A spreadsheet on the ombudsman’s website indicates most workers will receive a few thousand dollars but some will get significantly more, with one worker who did not get payment for their on-call overtime set to receive $141,717.66.

The airline will then have to make a “contrition payment” of 5.5% of the underpayments to the federal government.

An outside expert will then review the underpayments to make sure all employees have received what they are due.

Numerous Australian companies in the past year have reported they were not paying workers in compliance with Australia’s complex labour laws, including Wesfarmers, Commonwealth Bank, Super Retail Group, Michael Hill Jewellers and the ABC.

Qantas has been contacted for comment.

Shares in the company were 15.11% lower at $3.095 by 12.15 AEDT on Friday as the coronavirus-driven rout of the market continues apace.

Qantas shares have slipped 59% from an all-time high of $7.46 in December, during which time it has slashed flights and frozen its chief executive’s pay packet in a bid to soften the coronavirus blow.