While the two companies might lose clients due to the new law, it could have been much worse for ZTE. The Senate already voted to reinstate a ban that would continue preventing ZTE from working with American manufacturers. It could have been a death sentence for the tech giant, seeing as it relies on US chipmakers for parts. However, the House of Representatives passed a version of the Defense Authorization Act without the language that reinstates those sanctions. The two chambers worked on a compromise after the Senate gave up on trying to restore the ban, and this measure is what they came up with.
The US government considers Huawei and ZTE as security threats and has been seeing them as such for a long time. Back in 2012, the Congress published the results of an 11-month probe wherein the investigators noted how the companies failed to explain their ties to the Chinese government. Earlier this year, the Pentagon banned the companies' phones from military base retailers, citing security concerns. And just recently, the Democratic National Committee advised candidates running in November not to allow their staff to use devices by either company, especially after what happened during the 2016 Presidential Elections.