Two California men convicted of possessing marijuana without tax stamps - the first case of its kind in Utah - were sent to prison Monday and could face more than $770,000 in back taxes owed.

In a trial before 3rd District Judge Dennis Frederick, Kim Robinson and Francis Xavier Towers, both 36, were found guilty of possession of a controlled substance with intent to distribute.They were also convicted of "unlawful possession of marijuana without tax stamps affixed," a law passed by the 1988 Legislature.

On Monday, Frederick sentenced the men to terms of up to five years in Utah State Prison and fined them $6,250 each.

The convictions permit the Utah State Tax Commission to collect back taxes, which could exceed $770,000.

The men were in possession of 243 pounds of marijuana last April 12, when Utah Highway Patrol Trooper Anthony Garcia stopped their van on I-80 near 32nd East.

"None of the packaging containing the marijuana bore appropriate stamps, labels or other indicia demonstrating the tax . . . had been paid," according to a complaint filed by Garcia.

Attorneys for Robinson and Towers say the tax stamp law is unconstitutionally vague and that they plan to appeal.