Members of the National Union of Journalists at BBC Wales are taking part in industrial action.
The walk-out began at midnight and is the first of two one-day strikes over potential redundancies at the BBC.
The union is protesting against compulsory redundancies due to cutbacks in funding.
A spokesperson for the BBC said it was working to reduce compulsory redundancies but some were likely due to the reduction in funding.
NUJ members picketed outside Broadcasting House in Llandaff in Cardiff.
Spokesman Martin Huws said: "Management have acted with indecent haste, haven't followed proper procedures, they've got rid of someone in the World Service even though there were redeployment opportunities.
"Nobody wants to go on strike. Nobody wants to lose a day's pay but management's attitude means they leave us with no option."
The BBC said it was "disappointed" that the NUJ called the strike and apologised to audiences for any disruption to services.
A spokesperson said: "Industrial action will not alter the fact that the BBC is faced with a number of potential compulsory redundancies, following significant cuts to the central government grants that support the World Service and BBC Monitoring.
"We will continue with our efforts to reduce the need for compulsory redundancies, however, the number of posts that we are having to close means that unfortunately it is likely to be impossible for us to avoid some compulsory redundancies."