Ofcom has opened an investigation into how the Premier League sells live TV media rights for its football matches in the UK.
It follows a complaint from Virgin Media, which was submitted to Ofcom in September.
BSkyB and BT currently share the rights to televise Premier League football games.
The price for the latest rights deal - covering 2013-16 - rose by 70% to £3bn when it was announced in 2012.
Ofcom investigates where there are reasonable grounds for suspecting an agreement may be intended to prevent, restrict or distort competition.
It says the probe will be carried out under the terms of the Competition Act.
The Premier League will soon be starting the bidding process for the next tranche of rights from 2016 onwards.
But Virgin claims that the current arrangements "for the collective selling of live UK television rights by the Premier League for matches played by its member clubs is in breach of competition law".
In particular, it has raised concerns about the number of Premier League matches for which live broadcasting rights are made available.
"Virgin Media argues that the proportion of matches made available for live television broadcast under the current Premier League rights deals - at 41% - is lower than some other leading European leagues, where more matches are available for live television broadcast," said Ofcom in a statement.
Ofcom said it was "mindful of the likely timing of the next auction of live UK audio-visual media rights, and is open to discussion with the Premier League about its plans".
It also says it will look at the issue of how many games are moved from their traditional 3pm kick-off times on Saturdays, because of TV scheduling needs.
As part of this, it will approach the Football Supporters' Federation and certain other supporters' groups to understand their views.
When Virgin's initial complaint was made, the Premier League said its audio-visual rights had "always been sold in a transparent and open process".
"Regulators have examined our rights packaging and sales process in considerable detail in the past and found both of them to be compliant with UK and European competition law."
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