The UK communications regulator is investigating TalkTalk, amid concerns that the internet service provider (ISP) may have mis-sold its fixed phone lines.
Ofcom said it had received a number of complaints about the behaviour of the broadband provider, which currently requires broadband bundle customers to also take a TalkTalk phone line.
The news comes as another blow to the ISP, which was recently accused of issuing broadband bills to customers who had already cancelled their contract.
In a statement issued to the Reuters news agency, the TalkTalk said it was "fully cooperating" with Ofcom as it conducts its investigation, and would make all relevant information available to the regulator.
"We continually review our sales processes and take any potential issues of mis-selling extremely seriously," the ISP stated.
Customers signing up for a TalkTalk broadband package, such as the entry-level Essentials deal, are required to take out a phone line as the ISP's broadband services are provided over the same unbundled network, reports ISPreview.co.uk.