A Polk County judge has dismissed a lawsuit filed by one of Iowa's largest labor unions challenging the constitutionality of the state's new collective bargaining laws.

The American Federation of State, County and Municipal Employees Iowa Council 61, which represents 40,000 Iowa government workers, filed the lawsuit in February just after former Gov. Terry Branstad signed into law sweeping changes limiting public-sector union workers' ability to collectively negotiate for better pay and benefits.

"While we are disappointed that this initial ruling in our fight for collective bargaining justice was not in our favor, we knew from the day we filed this lawsuit ... that this case would likely end up in the Iowa Supreme Court," AFSCME Council 61 President Danny Homan said in a statement. "We are exploring the next step in the legal process, including an appeal."

Under the new law, most public-sector union contract negotiations are now limited only to base wages. However, bargaining units with at least 30 percent of their members classified as public safety employees are able to negotiate for a broader range of issues.

AFSCME argued that violates the state Constitution's equal protection clause by creating groups of government workers receiving disparate treatment.

However, there is a high legal burden to prove laws are unconstitutional.

"The statute is presumed constitutional unless the challenging party meets its burden to negate every reasonable basis for the classification that might support disparate treatment," Chief District Judge Arthur Gamble wrote in his order outlining the legal principles governing the case.

The state argued a reasonable legislature could have decided that preserving bargaining rights for some public safety workers is necessary to prevent strikes or labor unrest, which could endanger the public in cases of emergency.

Actual proof of that justification is not necessary. But the court found it to be a credible rationale for the Legislature's decision.

Both AFSCME and the state were seeking summary judgment, which asks a judge to decide that a case can be settled based on existing facts and does not need to proceed to trial. Gamble found in favor of the state's motion and against AFSCME's. He dismissed the case.

AFSCME has 30 days to file an appeal.

"As proven by last week’s recertification victories, we’re not going anywhere," Homan said in the statement.

Last week, 436 out of 468 eligible public-sector bargaining units voted to recertify their organizations under new rules instituted by the collective bargaining changes.

The new rules require bargaining units to undergo elections before negotiating each new contract, and they must win a majority of votes from all employees covered under their contracts — not just a majority of people who vote in the election.

Database: Iowa Public-Sector Union Recertifications

"We’re in this for the long haul and look forward to the day that this unconstitutional law is overturned for Iowa’s public employees," Homan continued.

Monday's ruling comes about a week after a different judge tossed out a similar lawsuit brought by the Iowa State Education Association.

Brenna Smith, a spokeswoman for Gov. Kim Reynolds, praised the outcomes.

"Two experienced and highly-respected district court judges have now dismissed these cases," Smith said in a statement. "Last session, the Legislature updated Iowa's 43-year-old collective bargaining law to bring fairness for Iowa taxpayers and flexibility to local governments, schools and state government to manage their resources with the opportunity to reward good public employees."