The Wall Street Journal cited people familiar with the matter in its report which said the ongoing probe, on the grounds of national security, would add to the pressure on the embattled company.
The report said there was no indication how far along the probe had progressed, nor what specific charges were being investigated.
Contacted for comment, a Huawei spokesman told iTWire: "Huawei has no comments on this issue. Huawei complies with all applicable laws and regulations where it operates, including the applicable export control and sanction laws and regulations of the UN, US and EU."
As a penalty, US firms cannot sell parts to ZTE for seven years.
Also last week, iTWire reported that Huawei and ZTE would not receive any subsidies from the Universal Service Fund that the US uses to subsidise equipment bought by rural and small carriers, and Huawei is reportedly cutting back US sales efforts as a result.
The US Federal Communications Commission decided to go ahead with the plan, despite objections from the Rural Wireless Association, a body that represents rural wireless ISPs that offer home or mobile Internet service and have fewer than 100,000 subscribers.
The US began its efforts to force Huawei out of local contracts after a 2012 Congressional report alleged the company was a threat to national security, with a warning that Beijing could use its equipment for state-sponsored spying or cyber attacks.
In December, President Donald Trump signed a bill to ban Huawei and ZTE equipment from nuclear weapons systems in the US Defence Department. Trump also banned a takeover of US processor maker Qualcomm by Singapore-based Broadcom because of national security concerns; Huawei's ties to Broadcom were mentioned as a concern.
Last year, multinational electronics corporation Best Buy said it would no longer stock the company's smartphones.