The investigation centers on allegations that Huawei stole trade secrets from USA business partners, including the technology that T-Mobile used to test smartphones, according to the Journal's report that cited people familiar with the matter.
It comes as the Trump administration is pressing China to take action on questions of technology theft or face additional trade tariffs.
Chinese firms have always been accused of engaging in intellectual property theft-something the Justice Department said it was clamping down on last November by working alongside the Federal Bureau of Investigation.
The investigation is tied to civil suits filed against the Chinese telecom giant, including a 2017 case in which Huawei was found liable for stealing technology from Bellevue-based T-Mobile, people close to the matter said.
The arrest of a Huawei employee in Poland last week underscored the increasing pressure on the company in the U.S., Europe and elsewhere over espionage concerns.
It's the latest signs of a growing technological cold war between the United States and China over telecommunications technology.
Huawei is the world's biggest producer of telecommunications equipment.
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Both have also been accused of failing to respect United States sanctions on Iran. T-Mobile didn't immediately respond to a request for comment.
The Handelsblatt daily reported earlier that the German government was actively considering stricter security requirements and other ways to exclude Huawei from the buildout of 5G mobile networks.
They told the newspaper the investigation was prompted in part by lawsuits against Huawei. That includes having Canadian authorities detain its chief financial officer (and daughter of its founder, Ren Zhengfei) Meng Wanzhou for extradition on charges she oversaw a byzantine, fraudulent scheme to evade sanctions on Iran, a move that infuriated the Chinese government.
In August, Donald Trump signed legislation banning government agencies from using services from Huawei and ZTE, among other Chinese entities.
"Huawei is effectively an intelligence-gathering arm of the Chinese Communist Party whose founder and CEO was an engineer for the [Chinese] People's Liberation Army", Cotton said.
She also blasted US legislators for proposals to block sales of American components to Chinese telecom companies, saying it amounted to "hysteria". She is awaiting extradition hearings to the US while living under restrictions in her million-dollar Vancouver home.
Huawei said in a statement the company and T-Mobile settled their disputes in 2017 following a USA jury verdict that found "neither damage, unjust enrichment nor willful and malicious conduct by Huawei in T-Mobile's trade secret claim".