The British government toughened its stance on Rupert Murdoch's $15 billion takeover of Sky, sending shares in the pay-TV group down sharply on fears it would take longer, and be more difficult, to complete.
British Media Secretary Karen Bradley had already said it would ask the competition regulator, the CMA, to examine whether the deal would give Murdoch's Twenty-First Century Fox too much control over the media.
On Tuesday she said she was minded to also ask for a six-month investigation into whether Fox would uphold broadcasting standards, following complaints over the management of Fox News in the United States.
Shares in Sky fell 4 percent on the unexpected twist.
"I have taken careful account of all relevant representations ... and have, today - as required by the legislation - written to the parties to inform them I am now minded-to-refer the merger to the CMA on the grounds of genuine commitment to broadcasting standards," she told parliament."
Fox, which already owns 39 percent of Sky, agreed a deal to buy the company in December last year.