LINCOLN, NE &#8211 More than 400 current and former Nebraska State Troopers have filed a federal lawsuit accusing lawmakers of violating their labor contract by forcing them to pay more into their pension plan.

The lawsuit alleges that when the Legislature increased troopers’ contribution rate to 19 percent as of July 1, up from the 13 percent they paid in 2009, it violated the U.S. constitution’s contract clause, which prevents states from enacting laws that retroactively impair contract rights.

The troopers are asking a judge to invalidate the rate increases and order Nebraska to reimburse the troopers for the state contributions they should have received, their attorney Gary Young said Tuesday.

A call to the Nebraska Attorney General’s office was not immediately returned Tuesday. Young acknowledged that state officials had not yet been served.

The lawsuit alleges that lawmakers illegally raised the monthly employee contribution rate, which was set at 8 percent when the most senior plaintiff joined the Nebraska State Patrol in 1977. The troopers “did not understand or agree at any time that their retirement pension would or could be changed in terms of the percentages of monthly salary contribution,” the lawsuit states.

The lawsuit was first reported by The Lincoln Journal Star.

Scott Black, a member of the State Troopers Association of Nebraska, said troopers contribute an average of about $1,000 a month to the retirement plan. The defined benefit plan is financed through both state and employee contributions.

“A trooper cannot decide to skip a month in order to pay bills that have piled up, care for a sick child, or make a down payment on a house,” Black said.

Black said the troopers filed the lawsuit because state law prevents them from collectively bargaining on their retirement accounts.

The State Troopers Association of Nebraska referred questions to Young, who represents the union.

Young said state law prevents the Legislature from changing the plans in a way that disadvantages the troopers, unless they offset it in some other way. The mandatory contribution increase on troopers who were already employed violated their contract, he said.

The lawsuit names Gov. Dave Heineman, Director of Administrative Services head Carlos Castillo, State Treasurer Don Stenberg, and former State Treasurer Shane Osborn as defendants. It was filed on behalf of 423 current and former state troopers.