Microsoft, Sony and Nintendo are being investigated in the UK for the way subscriptions to their online gaming services are renewed.
The Competition and Markets Authority (CMA) said it was “concerned” about whether the firms are acting legally.
The CMA will also look at the firms’ terms and conditions, as well as how they handle cancellations and refunds.
It is seeking testimony from customers about how they have been treated by the games companies.
The CMA said its investigation was at an “early stage” and it had not yet formed a view as to whether the companies have broken consumer protection law.
In a statement, Microsoft said: “We have received a notification from the Competition and Markets Authority and will be co-operating fully with their investigation.”
Nintendo and Sony have not yet responded to a BBC request for comment.
One key focus of the investigation was the widespread use of so-called “roll-over” contracts which automatically resubscribe customers at the end of a contract’s term.
“Roll-over contracts are becoming more and more commonplace and it’s essential that they work well for customers,” said CMA boss Andrea Coscelli in a statement.
Mr Coscelli added that the CMA wanted to be sure that customers were being treated fairly when contracts are automatically renewed.
He added that the investigation was part of work the CMA was doing in response to a “super-complaint” by Citizens Advice about what has become known as the “loyalty penalty”.
This can affect customers who stick with a brand for a long time, not only in gaming, because of costly exit fees or lengthy and difficult exit processes.
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