Despite objections from a number of human rights groups, Colombia’s Congress approved a constitutional amendment giving military courts greater jurisdiction over crimes committed by armed forces members.

Colombia’s military has a checkered human rights record that has in the past led U.S. lawmakers to selectively withhold aid from tainted units.

Winning final approval in the Senate by a 57-7 vote, the law is widely considered a gesture by President Juan Manuel Santos to placate the military brass, whose support he needs in peace talks with Colombia’s largest leftist rebel group to end a half-century-old conflict.

Santos is expected to sign the legislation this week.

José Miguel Vivanco, Americas director for Human Rights Watch, called the amendment “an unnecessary and premeditated blow to human rights.”

“It creates a serious risk of ‘false positives’ and other military atrocities remaining unpunished,” he said. “False positives” refer to killings by soldiers of civilians, often lured into traps with promises of employment, who are later dressed up as leftist rebels to increase units’ body counts.

There are hundreds of such cases from the 2000s that coincided with major battlefield gains by Colombia’s U.S.-backed military against the leftist Revolutionary Armed Forces of Colombia, or FARC. Colombian military units have also colluded with right-wing death squads responsible for the killings of thousands of suspected rebel sympathizers.

“‘False positives’ are going to end up outside the civil justice system and there’s no way around it,” said Sen. Parmenio Cuellar of the leftist Polo Democratico party and a former justice minister.

Vivanco lobbied successfully to include language in the amendment that specifies military courts can under no circumstances try cases of crimes against humanity or violations of international humanitarian law, including forced disappearance, sexual violence, torture, forced dislocation and extra-judicial executions.

However, rights activists and leftist lawmakers failed to persuade the bill’s sponsors to replace “extra-judicial executions” with the exact names of crimes that are defined in the legal code, such as murder and aggravated murder. Because “extra-judicial execution” is not a crime in the legal code, critics fear hundreds of cases of extra-judicial executions would be transferred from civilian to military courts.

The bill’s sponsors say that won’t happen.

“This is not an instrument of impunity,” said Sen. Juan Manuel Galán, son of the presidential candidate Luís Carlos Galán who was assassinated in 1989 by drug lords. “If cases have no relation with (military) service they should immediately go to civilian courts.”

A clause in the constitutional amendment gives authorities a year to determine which prosecutions should pass to military justice.

More than 1,700 extra-judicial execution cases involving nearly 3,000 deaths, the vast majority committed in 2002-2008 during the presidency of Alvaro Uribe, are currently working their way through the civilian justice system.

A scandal over the uncovering of those cases, which the United Nations later called systematic, prompted Uribe in October 2008 to fire three generals and 17 other officers for negligence. The army chief, Gen. Mario Montoya, resigned the next month.

Santos was defense minister at the time.

Rights activists also oppose another element of the amendment that creates a special court comprised of four civilians and four retired military officers that will decide jurisdictional disputes among civilian and military justice systems.

After Santos’ signs the law, it is subject to review by the Constitutional Court, which could take months.

The peace talks with the FARC began in November in Cuba after six months of secret talks and Santos has said he will give them a year to succeed or fail.