A media workers union has said the BBC plans to dismiss some staff in Bristol working on Casualty to try to "prevent them accruing employment rights".
A Bectu spokesman said it understood seven of a team of 12 props staff were about to lose their jobs after 11 months and two weeks of service each.
The BBC last year confirmed that the filming of the television programme would move from Bristol to Cardiff.
The corporation said it could not comment on specific negotiations.
Certain employment rights are secured by UK staff employed for more than 12 months.
Filming on Casualty is expected to start in Wales next year. Bectu says some of the group's employment is due to end on Saturday.
Affected workers held a protest earlier outside the production studios on St Philips Road.
A petition is in circulation and Bectu said it was encouraging staff at risk to lodge a formal appeal.
A union spokesman said: "The BBC's stance is so unfair and so wrong it has to be challenged publically.
"The experience represented by the staff at risk cannot be replaced locally and it is predicted that production managers may need to hire staff from London."
He added that some of the affected staff had worked on Casualty for up to six years. They were contracted by Bristol Design Services until April 2009, when they were taken on by the BBC, he said.
A BBC spokeswoman said the organisation did not comment on specific negotiations.
She said: "The fixed term and freelance workforce are extremely important and very much valued at the BBC, providing the flexibility needed to respond to the dynamic and project-oriented nature of programme making.
"We are committed to continue an open dialogue with Bectu to ensure that fixed term staff and freelances are appropriately engaged and recognised for the critical contribution they make."