BANGOR — The former manager of a buffet-style Chinese restaurant in Brewer that has been the target of a federal investigation since 2006 was sentenced Tuesday in U.S. District Court to 15 months in federal prison on multiple charges related to employing and harboring undocumented workers.

Mei Ya Zhang, 29, of Waterville pleaded guilty more than a year ago to one count each of conspiracy and aiding and abetting the harboring of illegal aliens for commercial advantage and private financial gain, money laundering conspiracy and conspiracy to file false employer’s quarterly federal tax returns, according to the U.S. attorney’s office.

In addition to prison time, U.S. District Judge John Woodcock sentenced Zhang to three years of supervised release after she completes her prison term. Zhang, who is a U.S. citizen, also was ordered to pay more than $88,000 to the Internal Revenue Service for unpaid employment taxes.

She was ordered to report to prison on Sept. 16.

Zhang was arrested in January, more than three years after the Twin Super Buffet was first raided in November 2011. She remains free on $10,000 unsecured bond.

The Twin Super Buffet closed Feb. 25, according to a previously published report. Zhang said in early February that U.S. Immigration and Customs Enforcement, Homeland Security and U.S. Customs and Border Protection agents came to the restaurant three times in a 13-month period but found no illegal activity.

Zhang said in February that she planned to work in the family’s Waterville restaurant.

By pleading guilty, she admitted that between 2006 and 2011, the restaurant she managed brought undocumented aliens to Brewer.

“(Zhang) had them work six days per week, eight to 10 ½ hours per day, housed them in squalid conditions at a residence on Elm Street in Brewer, transported them back and forth each day to work, paid them under the table with cash generated illegally by the employment of undocumented aliens and filed numerous false quarterly employment tax returns in which the undocumented aliens were not disclosed and employment taxes were not properly withheld or paid,” a news release issued Tuesday by the U.S. attorney’s office said.

“The investigation revealed that about half of the employees at the buffet over that period were undocumented, and that the defendant’s activities concealed about $400,000 in wages and thwarted the collection of about $88,000 in employment taxes,” the release states.

The Zhang family owns the New China Super Buffet in Lewiston, the Super China Buffet in Waterville and the Kon Asian Bistro in Portland. It also owns five restaurants in Massachusetts and two in Rhode Island.

Zi Qian Zhang is the family patriarch and resides with his wife, Ai Hui Lu, in Massachusetts, according to court documents.

Mei Ya Zhang, who is the niece of Zi Qian Zhang, was the first family member in Maine to be charged with a crime. Her sister, Mei Juan Zhang, 31, of Fairfield is serving a 14-month sentence at the Danbury Federal Correctional Institution in Danbury, Connecticut. She waived indictment and pleaded guilty to the same charges in April in federal court in Bangor.

The investigation, which began in February 2006, revealed that the Zhang organization employed and harbored scores of illegal aliens at its Chinese buffets and bistros, according to court documents. The family allegedly harbored them at 11 safe houses located near the restaurants and ferried them to and from work in vans.

Federal prosecutors in April asked a federal judge to order the owners of 11 Chinese restaurants in three New England states to forfeit more than $153,000 seized from bank accounts in Maine.

Assistant U.S. Attorney Donald Clark alleged in a complaint that the Zhang organization skimmed nearly $2.9 million in cash transactions from the businesses in Maine, Massachusetts and Rhode Island over a 10-month period. The Zhang family also hired and housed undocumented workers whom they paid in cash without withholding taxes, according to the complaint.

The Zhang sisters could have been sentenced to as many as 20 years in federal prison on the money laundering charge. On the harboring illegal aliens and filing false federal tax return charges, they each faced up to 10 years in prison. In addition, the women could have been fined a total of $1 million.