The executive order, issued by President Donald Trump in May 2019, under the International Emergency Economic Powers Act, allows the regulation of commerce as a reaction to a national emergency that is a threat to the US.
In the main, it was meant to block Chinese firms Huawei Technologies and ZTE Corporation from supplying equipment to American companies.
The US also placed Huawei and 68 of its affiliates on the Entity List, a blacklist that prevents a company from buying components that have more than 25% of content that is produced in America.
Some American companies which trade with Huawei have got around this by supplying the Chinese firm from their units outside the US.
That is now proposed to be blocked by a change in the Foreign Direct Product Rule which places some goods made abroad under US regulations if they are based on American technology or software or made using American equipment.
This latest step aims to block sales of some optical materials, radar equipment and semiconductors, among others. Additionally, specific restrictions have been proposed to limit Huawei from buying semiconductors from TSMC, which it uses in its HiSilicon chip-designing unit.
The US Department of Commerce has periodically given companies within the US extensions of a grace period to deal with Huawei. That period is expected to be extended again.
Only about 1% of gear used in US telecommunications networks is from Huawei with Ericsson and Nokia (48% apiece) having the major share and Samsung (3%) making up the remainder.