Huawei Technologies Co. and ZTE Corp. "cannot be trusted," U.S. Attorney General William Barr has said, labeling the Chinese firms a security threat as he backed a proposal to bar U.S. rural wireless carriers from tapping an $8.5 billion government fund to purchase equipment or services from them.

The Federal Communications Commission will vote on Nov. 22 and is proposing requiring the carriers to remove and replace equipment from the companies.

Barr wrote in a letter to the FCC released on Thursday that "their own track record, as well as the practices of the Chinese government, demonstrate that Huawei and ZTE cannot be trusted."