Thousands of supermarket staff working for Woolworths in the last seven years may have been underpaid.

A company spokesperson said a review in early 2022 identified two problems affecting salaried staff.

“We’ve made contact with around 5000 former or current salaried store team members who worked for us between 2015-2022 and who had roles that could potentially have been impacted by this.

“As we’re just starting this process, there isn’t enough information available for us to determine exactly which team members or stores may have been impacted and to what extent.”

In some instances, staff were not have been paid correctly for extra hours, or worked on days recorded as annual leave.

Woolworths had “proactively engaged” with the Ministry of Business, Innovation and Employment to fix the problem, she said.

“The majority of our 22,000 team members are not salaried and we expect a limited number of our total team to have been impacted by these issues. We expect any remediation owed to be paid out from mid-2024.”

But the union representing supermarket workers said some local Woolworths managers asked staff to do extra hours for free, or come in on their days off.

First Union chief executive Bill Bradford said these cases were not administrative errors.

“That was a very deliberate act by some … managers who said to people, ‘Go on leave, take a day’s annual leave but we want you to come back tomorrow and work without clocking in’.”

He said wage theft was common in many industries, and migrant workers are particularly vulnerable to this kind of exploitation.

However, the union was satisfied with the response from Woolworths senior leadership team since it became aware of the problem in 2022, Bradford said.