PORTLAND — A Brunswick man was sent to prison for a year and a day after he was convicted of attempting to defraud the Internal Revenue Service.

F. William Messier, 71, was sentenced Thursday in U.S. District Court on charges of conspiracy to defraud the U.S. by impeding and impairing the IRS and attempting to impede the lawful administration of tax laws.

Messier was also fined $15,000 and ordered to file tax returns and to pay income taxes dating to 2005, which was estimated by the government to be $168,376, not including interest and penalties.

Messier and a co-conspirator, David E. Robinson, were convicted in April after a five-day jury trial.

According to trial testimony, Messier, doing business as Oak Hill Communications, earned income generated on leases from telecommunication towers on his Brunswick property.

From 1999 through 2014, court officials said, Messier engaged in conduct intended to obstruct the enforcement of the revenue laws, including providing false tax documents to customers, obstructing IRS collection activities and the extensive use of cash. In 2012, the IRS assessed taxes and interest against Messier totaling $172,094 for the tax years 2000 to 2004.

Robinson claimed to be the “Interim Attorney General” of the “Maine Republic Free State” and advocated that people not pay federal and state taxes. According to the testimony of witnesses, after the IRS sent Notices of Levy to Messier’s customers, Robinson and Messier took a number of steps to obstruct and impede the IRS in the collection of the assessment, including presenting the IRS with a fake and worthless money order for the amount due by Messier.

According to witness testimony, Messier and Robinson urged customers not to honor the levies or to pay the IRS, and further urged customers to pay Messier in cash to conceal their payments from the IRS, sent false documents to the IRS and sent threatening and misleading correspondence to customers of Messier’s business urging them not to cooperate with the IRS. The two also filed civil lawsuits against some of Messier’s customers and employees of the IRS, which were dismissed in separate proceedings.

In imposing the sentence, Judge D. Brock Hornby said the notion that people do not have to pay federal taxes unless they live in the District of Columbia or a federal territory or are federal employees “is a fantasy.” People who believe this notion need to understand that their conduct is wrong and deserves a prison sentence and a fine.

The case was investigated by IRS Criminal Investigation.