Thousands of BBC journalists will go on strike tomorrow in a row over pensions, threatening disruption to radio and TV programmes.
Members of the National Union of Journalists (NUJ) will walk out for 48 hours, and again on November 15 and 16, and have threatened stoppages over Christmas.
The move followed a 70% rejection of the BBC's "final" offer on pensions, which the union described as making journalists "pay more, work longer and receive lower pensions".
NUJ general secretary Jeremy Dear said: "NUJ members across the BBC have consistently dubbed the proposals a pensions robbery. That hasn't changed. The BBC have now left members with no choice but to take action to defend their pensions."
Picket lines will be mounted at sites across the UK, including Bush House, Broadcasting House and the TV Centre in London.
The NUJ said it expected "widespread support" from journalists to the strike and predicted that members of other unions which have accepted a deal on pensions, could refuse to cross picket lines.
BBC director general Mark Thompson sent a message to staff today saying that the NUJ membership represented around 17% of the corporation's workforce.
"I believe that the package on pension reform which we have arrived at is a fair one and that it has changed in significant and positive ways as a result both of our consultation with staff and our discussions with the unions. To have gone further would have been to risk damage to the quality of our services to the public and to jobs. The proposals we agreed with the unions some weeks ago were and will remain the BBC's final offer.
"Some have argued that it would have been better if the whole question of pension reform had waited until after the formal valuation of the pension deficit had taken place. But the whole point of introducing the reforms now was so that the reforms could themselves be taken account of in the valuation process.
"As a result of the reforms, the deficit will be significantly lower than it otherwise would have been and the BBC's payments to eliminate that deficit will also be lower. Had we waited, the impact on services and jobs across the BBC would have been much worse."
Mr Thompson said he did not see "what earthly good" strikes were going to achieve, adding: "They may manage to take some output off the air or lower its quality. But strikes aren't going to reduce the pension deficit or make the need for radical pension reform go away.
"The BBC couldn't change its current position without breaking faith with the other trade unions and we just will not do that no matter how many strikes there are. For NUJ members, it will mean significant loss of earnings without any advantage or benefit in return, and the public, many of whom are facing difficult employment and economic pressures, will find it very hard to understand why the BBC's service to them should be impaired in this way.
"The BBC belongs to the British public and has a duty to deliver programmes and services of the highest quality to them every day of the year. They rely on us. We must not let them down."