U.S. lawmakers are urging AT&T Inc., the No. 2 U.S. wireless carrier, to cut all commercial ties to Shenzhen-based phone maker Huawei Technologies Co. and oppose plans by telecom operator China Mobile Ltd. to enter the U.S. market because of national security concerns, said two congressional aides.

The warning comes after the administration of U.S. President Donald Trump took a harder line on policies initiated by his predecessor Barack Obama.

Earlier this month, AT&T was forced to scrap a plan to offer its customers Huawei handsets after some members of Congress lobbied against the idea with federal regulators, sources said.

The U.S. Government has also blocked a string of Chinese acquisitions over national security concerns, including Ant Financial’s proposed purchase of U.S. money transfer company MoneyGram International Inc.

The U.S. lawmakers are also advising U.S. companies that if they have ties to Huawei or China Mobile, it could hamper their ability to do business with the U.S. Government, one aide said.

One of the commercial ties senators and House members want AT&T to cut is its collaboration with Huawei over standards for the high-speed next generation 5G network, the aides said. Another is the use of Huawei handsets by AT&T’s discount subsidiary Cricket, the aides said.

In 2012, Huawei and ZTE Corp. were the subject of a U.S. investigation into whether their equipment provided an opportunity for foreign espionage and threatened critical U.S. infrastructure — a link that Huawei has consistently denied.

“The next wave of wireless communication has enormous economic and national security implications. China’s participation in setting the standards and selling the equipment raises many national security issues that demand strict and prompt attention,” said Michael Wessel, a member of the U.S.-China Economic and Security Review Commission, which was set up by Congress.

U.S. lawmakers don’t want China Mobile to be given a license to do business in the United States, the congressional aides said. China Mobile applied for the license in 2011, and the application is pending before the Federal Communications Commission.

Huawei and Chinese telecom firms have long struggled to gain a toehold in the U.S. market, partly because of U.S. government pressure on potential U.S. partners. (SD-Agencies)