Supermarket Morrisons is being sued by staff after their personal details were posted on the internet.
They staff seek to make the supermarket chain liable after a member of staff stole the data of nearly 100,000 employees in 2014.
Andrew Skelton, an auditor at the firm's Bradford head office, is undergoing an eight year jail sentence since 2015, for the crime.
The workers are seeking compensation for the "upset and distress" caused but Morrisons has denied liability.
Jonathan Barnes, counsel for 5,518 former and current Morrisons employees, told justice Langstaff in London that the company had already been awarded £170,000 compensation against Skelton.
He added that according to the trial judge Skelton wanted to do the company "some real damage".
"The judge was sure that the employees were victims too, and it is those victims who have received no compensation for their distress or loss of control of the situation," Barnes said, BBC reported.
He added it was a "simple complaint" by the employees who were required to provide the information at the time of joining the firm.
"We say that, having entrusted the information to Morrisons, we should now be compensated for the upset and distress caused by what we say was a failure to keep safe that information," Barnes told the judge.
The trial would only decide whether Morrisons is liable for damages and there will be a second ''quantum'' trial to decide the size of damages if the firm is found liable.
The case is being made as a group litigation order, which allows multiple similar claims to be judged in the same case, much like the US class actions. However, claimants need to opt into a group litigation order, rather than opting out as in the US.