BBC staff balloted on strike over pensions
Unions representing staff at the BBC have sent out ballot papers to their members asking for strike action in a dispute over pensions.
In June, the corporation announced plans to overhaul its pension scheme to try and tackle a £2bn deficit.
If Bectu and the National Union of Journalists members vote to strike, action could take place as early as 9 September.
It means live events including Last Night of the Proms may be affected.
The BBC plans to broadcast the concert live on BBC Radio 3 and show the first half live on BBC Two and the second half on BBC One.
Luke Crawley, assistant general secretary of Bectu, warned that viewers could be left watching "dark screens" if the strike action was to go ahead.
"People at the BBC very rarely go on strike and with many shows being pre-recorded all that is needed is a manager to press a button to transmit it," he said.
"But it seems to me that this time there could be an impact and there may be dark screens. Anything live would be hard for the BBC to do because you can't pre-record a live event."
The corporation's pension proposals include closing its current final-salary scheme to new joiners and imposing a cap on the amount pensionable salaries of existing members can grow to 1% a year.
A BBC spokeswoman said: "We continue to believe that the proposals we are making will deliver a pension scheme that is sustainable, affordable and flexible for BBC staff and the licence fee payer.
"We know that staff have concerns about the proposed changes but we will continue to listen and try to address these during the 90-day consultation period."
Actors' union Equity said it had consulted its small number of members within the BBC scheme and decided not to ballot.