Phan Phan-Gillis, 55, was part of a trade delegation when she was detained at a border checkpoint in March.
Now her husband, Jeff Gillis, is asking President Barack Obama and the State Department to arrange her release. He denies the accusations against her.
The Chinese Foreign Ministry has said Phan-Gillis is being investigated on suspicion of threatening China's national security.
Although she has not been charged, she was formally arrested over the weekend and moved to a more secure detention facility in the southern city of Nanning, according to her husband, who said the arrest allows Chinese authorities to continue their espionage investigation.
Phan-Gillis, known as Sandy to family and friends, is a Vietnamese-American of Chinese descent who has lived in Houston for about 30 years.
Gillis, who until now has not publicly discussed his wife's situation, decided to announce her arrest this week because Chinese President Xi Jinping is visiting the U.S. Gillis said he hoped the timing of the publicity would pressure Beijing and Washington to act.