Land Rover has dismissed union concerns that jobs could go at the Solihull plant following the decision to end production at Jaguar in Coventry.
Around 8,000 people work at Land Rover in Solihull
Amicus fears that if not enough people volunteer for redundancy there, job cuts may be transferred to Land Rover, whose parent company is also Ford.
The US car giant said this month it was looking for 400 voluntary redundancies at Jaguar's Browns Lane site.
But a Land Rover spokeswoman says there are "no plans to spread the package".
Staff at Solihull voted last week to accept changes to working conditions.
Ford said these would safeguard the future of the Land Rover factory on Lode Lane by making it more competitive.
Measures include "bell to bell" working, where staff will not be able to down their tools until their shift is over even if they have filled their quota.
Tim Parker from Amicus said: "We're very concerned because over the last two years if you count up all the redundancy exercises across both the staff areas in Jaguar and Land Rover, they come from very sensitive areas.
"Things like product development, marketing and purchasing.
"We're worried about the future development of products at Land Rover and Jaguar."
The assembly of Jaguar models will transfer to the Castle Bromwich plant in Birmingham.
Up to 425 of workers at Browns Lane will move there while a further 310 will remain in Coventry to make wood finishes for Jaguar models.
Around 8,000 people work at the Land Rover site in Solihull.