Sainsbury's is among major businesses in the UK and US affected by a cyber-attack on a payroll system provider.
On Saturday, Kronos confirmed it was dealing with a ransomware attack on its computer systems.
Many companies such as Sainsbury's rely on Kronos to log, store and process the hours employees have worked.
The supermarket chain is understood to have lost a week's worth of data for its 150,000 UK employees. But it said they would be paid before Christmas.
Multiple departments, including payroll, human resources (HR) and accounting are now using historical data and working patterns to make sure employees are paid the correct amount on time.
A ransomware attack is when hackers gain access to a computer network and encrypt valuable data, asking for a ransom to make it useable again.
A Sainsbury's spokeswoman said: "We're in close contact with Kronos while they investigate a systems issue.
"In the meantime, we have contingencies in place to make sure our colleagues continue to receive their pay."
Kronos, run by the UKG company, from Massachusetts, supplies a range of cloud payroll services, including an automated payment system.
Some services would be offline for several weeks, it said, and customers should "evaluate and implement alternative business continuity protocols".
US supermarket chain Wholefoods and carmaker Honda North America use Kronos and were among those affected, NBC news reported.
Honda UK told BBC News it was unaffected.
A UKG official told BBC News: "UKG recently became aware of a ransomware incident that has disrupted the Kronos Private Cloud, which houses solutions used by a limited number of our customers."
It had taken immediate action to investigate and mitigate the issue, alerted affected customers and informed the authorities
"We recognise the seriousness of the issue and have mobilised all available resources to support our customers and are working diligently to restore the affected services," UKG added.