British retailers are stepping up efforts to tackle theft, but a key source of the problem may be right under their own noses: staff.

About 40% of retail theft is committed by employees in warehouses, in transit and in stores, according to a report by research consultancy Retail Economics and security technology firm Thruvision. The total value of items stolen by staff will amount to about £3 billion ($3.7 billion) this year alone.

Shoplifting has become a growing issue for retailers during the cost-of-living crisis with many increasing the use of body-worn cameras to protect their staff from thieves who can become aggressive when confronted. Companies including Tesco Plc, J Sainsbury Plc and Next Plc have grouped together with the police to tackle the issue.

Read More: Retailers Demand Crackdown to Stop Wave of Shoplifting

Theft by staff isn’t new, but it’s seldom discussed publicly by retailers. Most of the theft by employees takes place in sprawling warehouses. Around two thirds of retailers interviewed for the report believe that over the past decade the opportunity for crime in distribution centers has accelerated.

Just as the high cost of living in the UK has led to more theft by shoppers and organized gangs, so too has it placed a burden on retail staff. Two thirds of those surveyed said that the increase in employee theft was due to the burden of higher costs. The report suggests that over the past year staff have shifted to stealing smaller necessities like groceries and clothing.

Another issue is the tight labor market, with retailers pointing to their increased dependence on temporary staff.