WESTBROOK — A Massachusetts man under investigation for employing illegal aliens and housing them in sometimes squalid conditions is the owner of a Bridge Street house that was cited for safety problems and may have been used as a rooming house.

Zi Qian Zhang is the leader of an organization accused of money laundering and violations of immigration law, according to a complaint filed in federal court. The probe by federal and state law enforcement agencies is also investigating his wife, Ai Hui Lu, owner of Kon Asian Bistro in Portland, and other individuals, according to the document.

It’s believed that the couple, who live in Swansea, Mass., own at least 12 Chinese restaurants in Maine, Massachusetts and Rhode Island. Authorities contend that the Zhang organization has been employing illegal aliens at the restaurants, transporting them between the restaurants and “safe houses,” and using money from the businesses to make mortgage payments on the properties.

Immigration agents were seen at both Kon Asian Bistro and the Westbrook house Wednesday. According to media reports, immigration agents were also at the New China Super Buffet restaurant in Lewiston, a home in Brewer, the Twin Super Buffet in Brewer and the Super China Buffet in Waterville that day.

Employees of the Zhang organization indicated that they have to work 70 or more hours each week without overtime pay or benefits and that no taxes are withheld, according to the complaint. The couple’s restaurants include Chinese buffets that typically charge customers between $7 and $10 for unlimited amounts of food and where many of the transactions are in cash, according to the document.

The complaint filed in U.S. District Court on Wednesday was filed in support of the U.S. Attorney’s Office proposed seizure of an alleged safe house in Brewer.

Lu is listed in city records as the owner of Kon Asian Bistro. The Brighton Avenue restaurant, near the Westbrook city line, is not a Chinese buffet. It is pan-Asian in style, includes a bar and has more expensive offerings, with some entrees costing as much as $30. It has a sister restaurant in East Greenwich, R.I.

The restaurant was open for business Thursday and an employee said it had shut down only briefly the previous day. Its current license was issued in May.

During its first application process, in 2008, Corporation Counsel Gary Wood raised the issue of a possible connection between Lu and John Zhang, the owner and operator of Maine Super Buffet, which occupied the space now used by Kon Asian Bistro.

Lu’s husband, Zhang, uses the name John, Robert Greenlaw, a land surveyor that has worked with the couple, said Thursday.

Wood wrote that the city conducted 19 food inspections at Maine Super Buffet between January 2003 and January 2006 because of serious public health deficiencies. Seven of the inspections resulted in failing grades.

Zhang has been the owner of 100 Bridge St. in Westbrook since 2002, according to assessing records.

In a Aug. 13, 2010 letter, Westbrook Code Enforcement Officer Richard Gouzie told Zhang it appeared that the single-family home was improperly being used as a rooming house. Photos taken that summer show rooms with bunk beds and an area where bed frames made of two-by-fours are stacked up.

Zhang also ran afoul of code issues in February 2006, when the fire department called Gouzie to the property because of life-safety issues after frozen water lines in the basement burst. In his inspection report, Gouzie documented problems including water spraying on spliced wiring in the basement, walls blackened with mold, five-gallon containers filled with water in the attic because of leaks, missing roof shingles and beds and plastic blocking windows. According to Gouzie, the occupants worked at Maine Super Buffet. Gouzie wrote that 14 people left the house after he said no one could stay there in its current condition.

On Thursday, no one answered knocks at the doors of the house, although a Nissan Sentra with Maine plates and a 2012 New York inspection sticker was parked in the driveway. The blinds were drawn, and clothing could be seen hanging from one blind that was partially open. Glass in some attic and basement windows was broken and a few window screens were on the ground. The garage door was in need of repair.

Zhang and Lu could not be reached at any of the phone numbers on the license applications for Kon Asian Bistro or at the number linked to their Swansea address. The number listed for Chris Chan, the restaurant’s manager, wasn’t working and he did not return messages left for him at the restaurant. It was not clear whether the couple had a lawyer.