The $850 million sale of Cree Inc.’s Wolfspeed Power unit to German chipmaker Infineon Technologies may not happen, the companies said, citing U.S. government security concerns.

The reason is the U.S. move to stop the transfer of sensitive technology.

The companies did not say which technologies the U.S. government is worried about going to a foreign firm, but it could involve Wolfspeed’s devices with gallium nitride, which has military applications and has resulted in blocking of past acquisitions, Reuters speculates.

Infineon said in a statement that the Committee on Foreign Investment in the U.S. (CFIUS), which examines deals with security questions, told the companies it poses a risk to U.S. security.

“Against this background, Infineon is of the opinion that there is a considerable risk that the transaction, as agreed, is not going to close,” Infineon said.

It also said it will work with CFIUS to find a solution if possible.

Cree, (CREE.O) in a separate statement, said the companies are looking at alternatives to modify the deal and make it acceptable.