Four family members who operated a temporary firm in Lowell, Mass., received prison sentences for defrauding the IRS of more than $5 million, the US Attorney’s Office reported Tuesday. One defendant received a sentence of more than six years in prison.

The staffing firm provided unskilled workers to Lowell-area companies, including those in the packaging and food services industries. It reported $2.2 million in wages between 2004 and 2009 when the real figure was nearly $30 million, according to the US Attorney’s Office.

Workers were paid off the books from about 20 separate bank accounts — with 4,300 bank transactions in all — as part of a plan to avoid triggering reporting requirements, according to the US Attorney’s Office. Defendants also defrauded workers’ comp insurer, Granite State Insurance, by hiding the true number of temps to avoid $880,000 in insurance premiums, according to the office.

Defendants in the case, according to the office, were:

• Margaret Mathes, 67, who was sentenced to 80 months in prison.
• Bosea Prum, 47, who was sentenced to two years in prison. Prum is Mathes’ daughter.
• Sam Pich, 63, who was sentenced to two years in prison. Pich is Prum’s brother in law.
• Thaworn Promket, 52, who was sentenced to one year in prison. Promket is Prum’s husband.

All defendants were ordered to pay more than $6 million in back taxes and workers’ comp benefits. In addition, Mathes and Prum were also ordered to pay $100,000 within the next 45 days, according to the office. In addition, Prum and Promket must also pay more than $500,000 in additional back taxes for amounts underreported on their personal tax returns.

All four pleaded guilty to defrauding the IRS, mail fraud and structuring monetary transactions to avoid reporting requirements in August 2010.

In addition:

• Prum also pleaded guilty to 10 counts of filing false employment tax returns, six counts of mail fraud and two counts of structuring monetary transactions.
• Pich also pleaded guilty to 17 counts of assisting the filing of false employment tax returns, six counts of mail fraud and two counts of structuring monetary transactions.
• Promket also pleaded guilty to seven counts of filing false employment tax returns, six counts of mail fraud and two counts of structuring monetary transactions.

Mathes and her daughter Prum also received an obstruction enhancement after Mathes greatly exaggerated Alzheimer’s symptoms in an effort to get a shorter sentence, according to the office.