Proposals to regenerate a town centre could be under threat after the government granted listed status to a theatre at the centre of the plans.
The listing could add millions to the regeneration costs
The Department of Culture, Media and Sport (DCMS) said the auditorium, stage and fly-tower of Billingham's Forum Theatre are to be listed.
However, there are fears that the move could add millions to the cost of developing the town centre.
But Save our Theatre campaigners say the listing status should be embraced.
Kevin Bowler from the group said: "The Forum is the jewel in the crown of Billingham and will help the regeneration of the town."
However, Kevin Pitt, chairman of the Billingham Partnership board, believes the listing has added £4.3m to the cost of redeveloping the town centre.
He said: "We're actually unsure who asked for the listing because we certainly didn't, and these people might want to come forward and explain how we're going to raise £4.3m to build the infrastructure."
Unless the Deputy Prime Minister overrules the decision by the DCMS, the auditorium, fly tower and stage cannot be modified.
Stockton Council said it was surprised at the listing decision and was considering how to respond.
Alex Cunningham, cabinet member for education, leisure and cultural services, said: "Inevitably, this will delay and put at risk the regeneration of Billingham town centre and we must understand that doing nothing is not an option."
The council said some details of the listing were confused, and it too was unsure who had requested it.