US President Donald Trump has declared a national emergency to protect American computer networks from foreign adversaries.
Mr. Trump signed an executive order which effectively bars US companies from using foreign telecoms believed to pose a security risk to the country.
Mr Trump does not name any company specifically in the order. However, analysts suggest it is mainly directed at Chinese telecommunications giant Huawei.
A number of countries – including the US – have raised concerns that the company’s products could be used by China for surveillance. Huawei has said its work does not pose any threat. The US is also embroiled in an escalating trade war with China.