Jaguar Land Rover will stop production for a full week due to uncertainties around Brexit.
Staff will not be required at its Castle Bromwich, Solihull, Wolverhampton and Halewood plants from today (Monday), with another closure planned for the week following Easter.
Jaguar Land Rover has been a vocal critic of the idea of leaving the EU without a deal and blamed growing uncertainty around the process for the shutdown. It has warned that a no-deal Brexit would cost the company more than £1.2 billion profit a year.
The union, Unite, said the shutdown was agreed in January when the UK was due to leave the EU on 29 March.
Mick Graham, Unite's convenor at Solihull, said: "We had to make some plans to protect the business as best we could and we started talking about this in January.
"We knew we had to take reactive action to mitigate the potential effect of a bad Brexit or no-deal Brexit.
"Suppliers need notice to get their parts across to us... It was a prudent thing to do."