SPRINGFIELD — After more than 15 months of contentious talks and rumblings of a first-ever strike, members of the state’s largest employee union ratified a new collective bargaining agreement with the state Tuesday.

The pact gives 35,000 public sector employees a general wage increase that averages 1.3 percent per year over the contract’s three-year term. Those eligible for step increases will receive them as scheduled, while workers with more than 10 years’ seniority will receive a $25 per month increase in longevity pay.

At the same time, members of the American Federation of State, County and Municipal Employees union agreed to higher health-care premiums, co-pays and deductibles, changes that union officials say will save the state some $900 million over the life of the agreement.

Voting on the agreement, which was reached last month, was under way for more than a week among prison workers, child protection employees, nurse aides, police dispatchers and environmental technicians.

“This new contract takes into account the state’s fiscal challenges, while also recognizing the vitally important work state employees do,” AFSCME Council 31 executive director Henry Bayer said.

The agreement came as union members were being told by AFSCME leaders to begin preparing to walk off the job for the first time.

Gov. Pat Quinn last year enraged union negotiators when he terminated the union contract.

The governor, a Democrat from Chicago, had been seeking tough concessions from the union, including higher health insurance costs and zero raises for the life of the three-year deal. The union had earlier agreed to take no wage hikes in the first year of a pact.

The union said 96 percent of its members voted in favor of the deal.

“While this contract doesn’t fully keep pace with the rising cost of living, it will help employees meet those costs,” Bayer said. “At the same time, it will help the state to address its economic challenges.”