United States commentators say the tone of the tweet is a dramatic shift for Mr Trump, who has consistently accused China of stealing U.S. jobs. The U.S. Commerce Department barred American companies from selling components to ZTE in April after it violated sanctions on Iran and North Korea and then misled the department.
The ban is the result of ZTE's failure to comply with an agreement with the US government after it pleaded guilty a year ago to conspiring to violate USA sanctions by illegally shipping USA goods and technology to Iran, the Commerce Department said.
ZTE said it is working with the Trump administration to reverse the sanctions and "forge a positive outcome in the development of the matters".
Trump's reversal will likely have a significant impact on ZTE's USA suppliers such as Qualcomm Inc and Intel Corp. While a stock exchange filing from the firm revealed it ceased its main operations following the sanction earlier this week, an unnamed official from the manufacturer told CNET that doing so "does not mean we're going away".
"If evidence now exists to implicate ZTE, we believe it is appropriate for Commerce to take immediate action", the lawmakers wrote in the letter, which was addressed to secretaries of President Barack Obama's Treasury, Commerce and State departments.
The ban is the result of ZTE's failure to comply with an agreement with the USA government after it pleaded guilty past year to conspiring to violate US sanctions by illegally shipping US goods and technology to Iran.
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ZTE announced Wednesday that "the major operating activities of the company have ceased".
The firm suspended operations earlier this month after USA authorities banned American companies from supplying to it.
Trump's statement on Sunday also comes days after USA and Chinese officials held high level trade talks, during which Beijing specifically brought up the restrictions on ZTE.
Last week, the company said that its earnings have surged, reporting a 39 percent jump in net income for the first quarter.
ZTE did not immediately respond to a request for comment.
ZTE is not among Qualcomm's publicly disclosed largest customers, which include Apple Inc, Samsung Electronics Co Ltd and Chinese smartphone makers Oppo and Vivo. ZTE provides services for 100 million users in India, 300 million users in Indonesia, and 29 million users in Italy, the official said.
During a meeting with seven high-level members of the Trump administration last week in Beijing, Chinese officials reportedly brought up the ZTE crackdown and urged the United States to ease up.