Nearly 800 employees of South East Queensland's water supplier have been underpaid by more than $7 million, with the final total yet to be established.
The Fair Work Ombudsman began investigating Seqwater in 2020 and found the Queensland government statutory authority failed to correctly record and pay overtime, as well as other entitlements.
The water authority has signed an enforceable undertaking and the regulator is overseeing the back-payment of 790 current and former employees for work completed between 2016 and 2022.
The affected employees were engaged in a range of administrative, technical and professional roles.
Fair Work said to date more than $7.75 million had been paid out, with individual payments ranging from less than $1 and and $380,000.
Most of the underpayments related to overtime pay, but other entitlements including travel, on-call and call-back allowances, remote assistance allowance, leave loading and ordinary hourly rates were also underpaid.
Seqwater also breached record-keeping and pay slip laws.
Further underpayments are still being quantified, but all employees must be paid by February next year.
Seqwater boss apologises to workers
Fair Work Ombudsman Sandra Parker said the authority had shown a strong commitment to rectify the underpayments.
"Seqwater's breaches and subsequent significant backpay bill demonstrate how important it is for employers to place a high priority on workplace compliance, including having a clear understanding of how any enterprise agreements apply and performing regular checks to ensure they are providing employees with all lawful entitlements," Ms Parker said.
The water authority will also have to pay $545,000 to the Commonwealth's Consolidated Revenue Fund.
Seqwater chief executive officer Neil Brennan apologised to underpaid employees in a statement, and said the authority had implemented a "comprehensive suite of controls" to ensure its compliance with its obligations.
"Our review has determined this issue was largely a result of complex and ambiguous enterprise agreements, and our payroll system," he said.
"We are nearing the end of repayments to both current and former employees.
"Paying our people correctly is of the utmost importance, I want to apologise to both our former and current employees who have been affected by this issue."