NIG's Manchester-based claims staff are to transfer to a new office and work on Tesco's claims.
The 30 personal-injury claims staff are to be relocated from the King Street office to the current Direct Line office in Quay Street. The move will see up to 200 Tesco Insurance sales, HR and claims staff concentrate in the Quay Street office by the end of April.
An NIG employee said: "I suppose something like this unavoidable but it seems to have come very quickly. People are feeling a little unsettled."
The future of the 40 remaining NIG underwriters in the King Street office remains uncertain with speculation they could be moved in the short term.
But the move was played down by NIG. A spokesman said: " Our aim is to maintain our presence in current locations, improve facilities for employees and at the same time provide a more dedicated focus on a business that forms a key part of RBS Insurance."