Defence giant BAE Systems said it is reviewing its warship business - but declined to discuss a report that it is considering closing the historic Portsmouth dockyard.
The Sunday Times said such a move would threaten up to 3,000 jobs and end more than 500 years of naval shipbuilding in the city.
It quoted senior industry sources as saying Portsmouth was the likely victim of a review of the group's shipbuilding operations.
The company employs about 1,500 at the yard and there are 1,500 jobs in support roles, it said.
BAE has yards on the Clyde, at Scotstoun and Govan, and at Portsmouth. All are working on hull sections for the aircraft carriers HMS Queen Elizabeth and HMS Prince of Wales, the newspaper said.
A company spokeswoman said: "As part of our business planning activity, we are reviewing how best to retain the capability to deliver and support complex warships in the UK in the future."
This would be in line with its commitments, she added.
"This work is ongoing and we will keep our employees and trade union representatives fully informed, as it progresses."