A dramatic standoff between Illinois’ largest state-employee union and Democratic Governor Pat Quinn ended Thursday morning with a tentative contract agreement after more than 15 months of negotiations.

For weeks, the American Federation of State, County and Municipal Employees Council 31 had been threatening to strike and urging its 35,000 members to prepare by setting aside extra cash and stocking up on medical prescriptions. Prison guards and others in public safety roles are legally barred from striking.

Rank-and-file members will have to ratify the contracts in a statewide voting process set to begin next week. The details of the tentative agreement have not been made public.