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A lawsuit challenging Michigan's law restricting funeral protests was filed Wednesday on behalf of a couple who were pulled over and arrested during a procession for a friend killed in Iraq because their van bore signs critical of then-President George W. Bush.

The American Civil Liberties Union says the 2006 state law is unconstitutional. It was approved with bipartisan support in response to an anti-gay church that has protested at funerals of U.S. soldiers killed in Iraq and Afghanistan.

"Although the Legislature may have had honorable motives in passing the law, this case is a textbook example of what happens when the state gives police officers unchecked power to arrest people who express unpopular views," said Michael Steinberg, legal director for the ACLU of Michigan.

The ACLU filed the federal lawsuit in Bay City against Clare County and two sheriff's deputies on behalf of a 64-year-old Army veteran Lewis Lowden and his late wife, Jean.

They were arrested in September 2007 in Harrison, about 140 miles northwest of Detroit, on their way to the burial of Army Cpl. Todd Motley, 23, of Clare, who died in Muqdadiyah of wounds suffered when a bomb exploded near his vehicle during combat.

The suit, which seeks unspecified damages from the county, says the Lowdens were close family friends. Jean Lowden home-schooled Motley in high school and Lewis Lowden took him on fishing and camping trips.

Lewis Lowden for years had taped homemade political signs to the inside windows of his van criticizing the president and government policies, the lawsuit said. They made statements such as "Impeach Cheney-Bush" and "G.W. Bush: The Reason Why Murphy Wrote His Law."

No one complained about the signs when the Lowdens arrived for the funeral, according to the suit.

But during the funeral procession, viewed by hundreds of onlookers, the Lowdens were pulled over and arrested. They missed the burial service. In a statement released by the ACLU, Lewis Lowden said he "can never express the shame and humiliation" he and his wife felt when they were arrested.

Criminal charges were later dropped; the ACLU said Motley's family had asked prosecutors to drop them.

A message seeking comment from the Clare County Sheriff's Department was not immediately returned Wednesday.

The federal government and at least 37 states have enacted funeral-protest laws in response to the Westboro Baptist Church's picketing of military funerals. The Rev. Fred Phelps and his followers claim U.S. combat deaths are God's punishment for the nation's tolerance of homosexuality. Some states' laws have been struck down.

Michigan's law makes it a felony to "disturb, disrupt or adversely affect" a funeral within 500 feet of the ceremony or procession. The ACLU says it violates free speech rights and is unconstitutionally vague.

"This is a law you would expect in a totalitarian regime but not in the United States," Steinberg said. He said the law could have been written narrowly to bar "true disruptions" of a funeral such as loud noise keeping people from being able to listen to the ceremony.

One of the law's sponsors, Republican Sen. Jud Gilbert of Algonac, said the Lowdens' case is "very unique." He said lawmakers were trying to stop protesters from hurling insults at grieving families and did not think of the scenario that played out in Harrison.

"We recognize the right of free speech, that people have a right to demonstrate," Gilbert said. "If something is not constitutional, I hope the court would give guidance of how we could meet their test."