Members of the National Union of Journalists have begun a 48-hour strike at the BBC in a dispute over proposed pension plan changes, according to BBC.
The NUJ, which has 4,100 members at the BBC, voted to reject the corporation`s "final" offer on pensions.
Radio 4`s Today programme was an early casualty but BBC1`s Breakfast News was going ahead. Further industrial action is planned for 15 and 16 November.
BBC director general Mark Thompson said the strike would not cut the deficit.
Broadcasting union Bectu, which includes technical and production staff, voted to accept the deal.
The journalists` union says it expects most BBC radio and TV news programmes will either not go out or be severely disrupted.
It says many well-known presenters will not turn up for work, nor will many reporters and producers.
NUJ members at the BBC are also set to observe an indefinite work to rule from Sunday, ensuring they take full breaks and only work their minimum prescribed hours.
The dispute stems from the BBC`s plans to reduce a £1.5bn pensions deficit by capping increases in pensionable pay at 1% from next April.
Under the BBC`s revised offer, the amount employees would have to pay into the pension scheme has been reduced from 7% to 6%.
In return, they would get a career-average benefit pension - based on the average salary over an employee`s entire career - that would be revalued by up to 4% each year. The previous offer was 2.5%.
When employees draw their pension, payments will increase automatically each year in line with inflation, by up to 4% - again up from a previous offer of 2.5%.
NUJ general secretary Jeremy Dear said in response to the deal`s rejection that, "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."
The NUJ said it "expected widespread support" from its members to take industrial action.
Bectu members said after last month`s ballot that the amended offer was "the best that can be achieved through negotiation".
But it added their position could be reviewed if the pensions deficit turned out to be less than £1.5bn.
In an e-mail to BBC staff, director general Mark Thompson said the action - which is due to begin at midnight - "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," he added.