Trinity Mirror's £126.7m deal to buy titles including the Daily Express and the Daily Star has been referred to the UK's media watchdog after the UK government intervened on the grounds of public interest.
UK Culture Secretary Matt Hancock confirmed he was stepping in amid concerns over editorial decision-making and independence, as well as the reduction in the number of views in newspapers.
His move to intervene in Trinity's plans to snap up a string of titles from Richard Desmond's media empire means the deal has now been referred to Ofcom to review the public interest considerations.
The UK's Competition and Markets Authority (CMA) must also report on jurisdiction and competition issues.
The two watchdogs have until May 31 to report back, after which Mr Hancock will decide whether to refer the takeover for an in-depth investigation or accept moves to address concerns.
"I invited written representations from the parties by 26 April and, having considered these, I have written to the parties today confirming my decision to issue a Public Interest Intervention Notice," the Minister said.
"The role of the Secretary of State in this process is quasi-judicial and procedures are in place to ensure that I act independently and follow a process which is scrupulously fair and impartial, " he added.
Mr Hancock said the public interest concerns were two-fold.
"The first public interest ground is the need for free expression of opinion, and concerns the potential impact the transfer of newspapers would have on editorial decision making. The second public interest ground is the need for a sufficient plurality of views in newspapers, to the extent that it is reasonable or practicable," he added.
The CMA has already been investigating the deal and whether it will substantially lessen competition in the UK media industry.
Under its planned takeover, Daily Mirror owner Trinity will stump up an initial £47.7m to Northern & Shell, followed by £59m between 2020 and 2023 and a further £20m in shares to the privately owned firm.
It marks a major shake-up of Britain's media landscape, bringing together politically left-leaning titles like the Sunday Mirror with more right-wing publications such as the Sunday Express.
Trinity Mirror will also seize control of Daily Star Sunday, celebrity magazines New! and Star, and a 50% slice of the Irish Daily Star.
The merged group would then own nine out of 20 national UK newspaper titles, with a 28% share of monthly circulation.
Mr Desmond acquired the Express titles in 2000 for £125m, but the industry has had to grapple with sliding advertising revenues.
Circulation of the flagship titles have also come under pressure, with the Daily Express and Daily Star falling 6.8% and 11.1% respectively in December.