The Office of Fair Trading (OFT) is launching an investigation into e-book pricing.
The investigation centres on "agency pricing", where publishers set their own online pricing rather than allowing web vendors to set their own sales prices for e-books, according to a report in the Wall Street Journal.
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"Following a significant number of complaints, the OFT has opened an investigation into whether arrangements that certain publishers have put in place with some retailers for the sale of e-books may breach competition rules," the regulator said in a statement.
The investigation is at an early stage and it should not be assumed that the parties involved have breached competition law, added the OFT.
It is unclear so far who made the complaint, despite several vocal opponents to the model. Amazon.co.uk previously said the agency model "was a damaging approach for readers, authors, booksellers and publishers alike," reported trade title The Bookseller.
The Competition Act 1998 prohibits agreements, practices and conduct that may have a damaging effect on competition in the UK. A similar inquiry was launched in the US last year.