Welsh firms are expected to suffer as almost all UK carmakers halt production to cope with the coronavirus crisis.
There are 120 factories in Wales employing about 18,000 people making parts for car companies.
The biggest - Bridgend's Ford engine plant - halts work on Wednesday and its 1,200 workers will be sent home on basic pay.
Ford says it will reopen in mid-April but it is due to close completely in the autumn.
Employees will be keen the closure date is not brought forward.
The plant makes engines for Ford cars assembled in mainland Europe and for Jaguar.
Tim Williams, of the Wales Automotive Forum, said firms which make components were holding meetings to decide whether to close in line with vehicle manufacturers.
"We are keeping in close contact with them and are concerned about how they handle the cuts in production as major plants are shutting down," he said.
So-called "just-in-time" production methods have radically reduced the stock factories hold.
As a result, if big car companies halt production, smaller suppliers feel the effects faster.
Chancellor Rishi Sunak's measures to pay towards firms' salary bills have been welcomed by the Society of Motor Manufacturers.
However its chief executive Mike Hawes said: "Ninety-nine percent of UK automotive output is now halted, meaning that thousands of businesses are counting their future not in months or weeks, but in days.
"We need these measures implemented swiftly," he said.