The ruling Tuesday by the Fourth District Appellate Court sends the issue back to the Illinois State Labor Relations Board.
The board decided in November 2016 that talks between the Republican administration and the American Federation of State, County and Municipal Employees Council 31 was at “impasse.” That meant that Rauner could impose employment conditions on the 30,000 state employees and the union could strike.
The appellate court found that the labor board wrongly failed to follow established practice in determining impasse.
The two sides have been without a contract since July 2015. The union authorized a strike in early 2017 .