TalkTalk has confirmed that three of its India-based call centre workers have been arrested.
The London-based telecoms provider said that it alerted police after carrying out a data security review.
However, a spokeswoman stressed that it had seen no evidence that the suspects had been involved with a high-profile cyber-breach last October.
Nearly 157,000 of TalkTalk customers' details, including bank account numbers, were stolen in the breach.
The unnamed suspects do not work for TalkTalk directly but are instead employed by Wipro, a local call centre provider, in Kolkata (Calcutta).
"Following the October 2015 cyber-attack, we have been conducting a forensic review to ensure that all aspects of our security are as robust as possible - including that of our suppliers," the company said.
"Acting on information supplied by TalkTalk, the local police have arrested three individuals who have breached our policies and the terms of our contract with Wipro. We are also reviewing our relationship with Wipro.
"We are determined to identify and deal effectively with these issues and we will continue to devote significant resource to keeping our customers' data safe."
News of the arrests was first reported by Channel 4 News.
The Indian company has said it has a "zero tolerance" policy on data theft.
"Wipro is working closely with the customer in the investigation and will continue to extend its full co-operation to the investigating authorities," it said.
"We are unable to comment on the matter that is currently under investigation."