Concord — A judge suppressed evidence against more than a dozen people who were charged with drug possession after being stopped and searched by Customs and Border Protection agents last summer in northern New Hampshire, according to a ruling released on Friday.

The group was arrested on Interstate 93 in Woodstock, N.H., at checkpoints about 90 miles from the Canadian border. Searches uncovered mostly small amounts of marijuana and other narcotics as part of what authorities said was a search for people living in the country illegally. The agents used drug-sniffing dogs.

The drugs were handed over to local police because the amounts confiscated didn’t meet the federal threshold for prosecution.

The American Civil Liberties Union argued that the agents used the dog-sniff searches in situations where New Hampshire law enforcement would have been barred from conducting similar searches. The state argued evidence seized in other states obtained by the federal agents is admissible in prosecutions of state criminal charges.

Plymouth District Court Judge Thomas Rappa ruled “the evidence was seized in violation of the constitutional rights recognized” under the New Hampshire Constitution.

He also ruled the checkpoints violated the Fourth Amendment to the U.S. Constitution, which prohibits unreasonable searches and seizures. Under that amendment, a border patrol checkpoint is unconstitutional if its primary purpose is to detect drugs. Rappa ruled it was clear the primary purpose of Woodstock police at the checkpoint was to accept illegal drugs confiscated by the customs agents and handle prosecutions.

“This decision is a victory for civil liberties,” New Hampshire ACLU legal director Gilles Bissonnette said.

A message seeking comment was left with a lawyer who represented the state in the case.