Several rival media groups have jointly urged the government to consider blocking media magnate Rupert Murdoch's attempt to take full control of BSkyB.
In a letter to Business Secretary Vince Cable they argue that, given Mr Murdoch's newspaper empire, the move could reduce diversity in the industry.
The signatories include the heads of the BBC and Channel 4.
Chief executives of newspaper groups, including the Telegraph, the Mail, the Guardian and the Mirror, also signed.
Mr Murdoch's company, News Corp, says it has not finalised its plans - and points out its critics are also commercial rivals.
News Corp has said it wants to take over the remaining 61% of BSkyB it does not own.
It currently owns News International, which owns the Sun, the News of the World and the Times and Sunday Times newspapers in the UK.
Together they account for more than a third of all national UK newspaper circulation.
The BBC's business editor, Robert Peston, reported last month that Mr Cable is likely to issue an "intervention notice" to media regulator Ofcom once a final offer is made.
This would order the watchdog to look at the impact of the takeover.
In June, News Corp told the board of BSkyB that it was prepared to pay 700p a share to take full control of the leading satellite broadcaster.
BSkyB's directors said the offer was £1 per share too low, but agreed to resume negotiations after regulatory hurdles have been cleared.
News Corporation has been confident that it could demonstrate that the combination of BSkyB with News Corporations' UK newspapers - the Sun, the Times, the News of the World and the Sunday Times - does not pose a serious threat to competition.
BSkyB is the biggest broadcaster in the UK. Its revenue in the UK was £5.9bn in the 12 months to June, which compares with the BBC's global revenues of £4.8bn.