But when a judge warned that unfaithful spouses could technically be sentenced to life in prison, an obscure and seldom-used provision of the state’s criminal law became the subject of international scrutiny.

It’s unclear how serious Judge William Murphy of the Michigan Court of Appeals was when he pointed out the possible consequences of extramarital sex. Some observers say the liberal judge was making a political point by taking a strict interpretation of the law to an absurd conclusion.

Others have suggested Murphy was trying to embarrass Michigan Atty. Gen. Mike Cox, whose office triggered the ruling by appealing for a harsher sentence for a man who traded drugs for sex. In 2005, Cox acknowledged having an adulterous relationship.

Murphy’s adultery bombshell was a footnote in a November ruling on a drugs-for-sex case. But since a Detroit Free Press columnist wrote about the footnote last week, blogs and radio talk shows have debated the pros and cons of life sentences for cheating spouses.

The ruling came in the case of Lloyd Waltonen, 43, a man from Charlevoix in northern Michigan, who supplied a cocktail waitress with the prescription painkiller OxyContin in exchange for sex. Last year, Charlevoix Circuit Judge Richard M. Pajtas sentenced Waltonen to four to 20 years in prison, but dismissed four counts of firstdegree criminal sexual conduct, punishable by a life term, on the basis that the sex was consensual.

The state attorney general’s office successfully appealed Pajtas’ ruling, citing an obscure provision of Michigan’s criminal law, which states that a sexual act committed at the same time as a felony constitutes criminal sexual conduct.

An appellate panel found Waltonen guilty of criminal sexual conduct. He has asked the state Supreme Court to consider an appeal.

In the opinion, Murphy wrote that although legislators may have drafted the law conceiving of scenarios in which there was a violent felony involving forced sex, he was "curtailed by the language of the statute from reaching any other conclusion."

Murphy wrote that a person was technically guilty of firstdegree criminal sexual conduct any time he or she "engages in sexual penetration in an adulterous relationship."

He noted that state law defines first-degree criminal sexual conduct as sexual penetration involving another felony. Because adultery is a felony, he wrote, adulterous sex could result in life imprisonment.

Such a sentence is unlikely. No one in Michigan has been charged with adultery since 1971.