Ofcom and the Competition and Markets Authority will examine 21st Century Fox's proposed £11.7 billion takeover of broadcaster Sky, the Government has announced.
Culture Secretary Karen Bradley told the House of Commons she has issued a European intervention notice on the grounds of "media plurality and commitment to broadcasting standards" linked to the bid from Rupert Murdoch's company.
Bradley told MPs that she had considered representations from the broadcasters but she was not satisfied that her concerns had been addressed.
While the representations from 21st Century Fox highlighted areas where it contested the position taken in my minded-to letter, none of the representations have led me to dismiss the concerns I have regarding the two public interest grounds I previously specified.
Bradley said that the regulator Ofcom would also conduct a "fit and proper" test into the corporate governance at the same time, after concerns were raised by MPs about the running of Murdoch's media empire.
She said: "On Monday Ofcom announced that it will conduct its fit and proper assessment at the same time it would consider any public interest test in response to my decision to intervene in the merger.
"This means Ofcom will conduct its assessment within the 40 working days it has to report to me on the public interests I have specified in the intervention notice.
"I welcome Ofcom's announcement - which will provide clarity for the parties but also provide reassurance to those who have expressed their own concerns about this issue - that this is a matter which Ofcom will now consider before the merger takes place."
Ofcom and the CMA will have until May 16 to investigate.
A 21st Century Fox spokesperson said it was keen to co-operate with the investigation and it was confident that the merger will be approved.