Several European parts plants and production lines have been shut down because of rare earth shortages caused by China imposing restrictions on exports, Europe’s auto supplier association CLEPA said, with the situation likely to worsen.

Of the hundreds of requests for export licenses made by suppliers since early April, only a quarter have been granted so far, CLEPA said, with some requests rejected on what the association described as “highly procedural grounds.”

“Procedures seem to vary from province to province and in several instances IP-sensitive information has been requested,” CLEPA said, adding that if the process was not streamlined soon, more plants would likely be affected in the next three to four weeks as inventories depleted.

CLEPA did not identify the companies that have shut down production.

The shortages threaten to cause havoc in the supply chains of automakers including Volkswagen Group, Mercedes-Benz and BMW, as well as suppliers including Robert Bosch and others that rely on rare earths for applications such as motors for electric cars.