Gull has issued a warning to its petrol stations not to dock workers' pay when customers drive off without paying.
A Masterton Night 'N Day franchisee has been accused of deducting paypackets of a staff member to cover the cost of petrol drive-offs.
Night 'N Day Foodstores Limited hold a management agreement over 21 Gull outlets.
Since the first report from employee Kerry McIvor, other workers have come forward to say their pay had been docked by their boss for drive-offs.
Gull said in a statement today that it had reimbursed Mr McIvor for the wage deductions made and "significant steps are being taken to ensure franchisees do not deduct pay from employees for drive offs".
"We will be reviewing the policy to leave no room for interpretation," said Dave Bodger, general manager of Gull New Zealand.
"Gull's policy is not to charge staff for drive-offs that happen on their shift and we have contacted all Gull branded sites across the country to reiterate this policy and ensure that it does not happen again.
"Craig Wright worked for the Masterton Night 'N Day and said he had his pay docked for drive-offs, too.
He told TV3 he thought he was owed around $1000 in pay deductions.
"When I had a drive-off I didn't have any pay that week. I didn't get paid for weeks on end.
"An investigation has been launched and Gull was looking in to the situation, gathering information from Night 'N Day, the franchisee in Masterton and other sites around the country.
"Not only do we want to get to the bottom of what has happened, we want to ensure this is an isolated incident.
"Mr Bodger said the company was "very disappointed and sorry" for the wage deductions taken from Mr McIvor's pay cheque.
"Night 'N Day chief executive Tony Allison has spoken to and apologised to Kerry and we too have called Kerry but are yet to speak with him to apologise. We can confirm that Kerry has been sent reimbursement for his deducted pay," Mr Bodger said.
A University of Canterbury business and economics associate professor said she was not surprised that petrol business owners would make their staff pay for loss of income due to customers not paying their petrol. Associate Professor Annick Masselot said the practice was neither acceptable nor legal.
"There seems to be a lot of grey practice areas in terms of pay," she said.
"Our workforce, especially when they are precariously employed, with low skills and low education, do not often know the rights they have or how to implement them.
"Often also they think that if they challenge their employers they will be at risk of losing their job. And they do run that risk.
"She said increasing union representation would combat the issue.
Jeff Sissons, Council of Trade Unions General Counsel, said: "Clauses in employment agreements allowing employers to deduct money from workers' wages to compensate them for loss caused by workers are unlawful. In the case of petrol station drive offs the worker will not even be at fault so deducting pay will almost certainly be against the law."
Mr Sissons encouraged workers to join a union.