Magna Seating has played a key part in the city's Transit van production line over the years from its base next door to the historic Ford factory in Swaythling.
But bosses have now pulled the plug on their Hampshire branch, admitting that “there is no longer a viable business case” for the facility.
The decision has been blamed on plans by Ford to axe its Southampton operation with the loss of 500 jobs.
Staff at Magna have been informed of the decision, but a date has yet to be set for closure.
A spokesman said: Magna Seating, an operating unit of Magna International Inc., has communicated to its workforce a plan to close its facility in Southampton, England.
“The difficult decision, which affects 30 permanent employees, is in response to Ford Motor Co.'s announcement that it is closing its Southampton Body and Assembly facility. Timing of the Magna Seating closure will be determined based on completion of the customer's requirements.
“Magna Seating Southampton is a facility dedicated primarily to the just-in-time manufacture and delivery of complete seating systems for the Ford Transit.
"As Ford works to restructure its Europe manufacturing operations and has subsequently announced plans to close Southampton Body and Assembly, there is no longer a viable business case for Magna Seating Southampton.
“Magna Seating will assist, where possible, with the transfer of employees into other Magna facilities where there are openings.”