System allowed managers to track how long employees were spending away from their desks and the amount of time taken to complete tasks
Barclays is under investigation by the privacy watchdog after allegations the bank spied on staff using computer monitoring software.
The system allowed managers at the lender to track how long employees were spending away from their desks and the amount of time taken to complete tasks.
Barclays used a program from Sapience Analytics to monitor staff anonymously for 18 months, but switched on an extra function in February allowing bosses to pick out individual employees.
The lender stopped managers from monitoring individual workers' data later that month and alerted the Information Commissioner's Office, after uproar among its workforce.
An ICO spokesman confirmed a formal investigation is ongoing and said: "People expect that they can keep their personal lives private and that they are also entitled to a degree of privacy in the workplace. If organisations wish to monitor their employees, they should be clear about its purpose and that it brings real benefits.
"Organisations also need to make employees aware of the nature, extent and reasons for any monitoring."
The ICO could not confirm when the investigation will conclude. If found to have breached data privacy laws, the bank faces a maximum fine of up to £865m.
It comes amid growing fears that employees are being monitored as they work from home using so-called "productivity tools" which allow managers to watch employees' laptop screens and monitor what they view online.
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Barclays declined to comment.