The Illinois Educational Labor Relations Board sided with the Chicago Public Schools Thursday, agreeing to move ahead with seeking injunctive relief to block future Chicago Teachers Union strikes like the one stage earlier this month.

CPS brought a complaint to the labor board in response to CTU's one-day strike on April 1 over unfair labor practices. The district argued that the one-day strike was illegal because the fact-finding process in contract negotiations had not yet been completed. For its part, CTU officials said the April 1 strike was a "one-day job action" over unfair labor practices, and something the union had "no intention of doing again."

The labor board issued a 4-1 decision in favor of the school district Thursday.

"We need to make it clear to the union that illegal work stoppages will not be tolerated," the Illinois Educational Labor Relations Board's General Counsel Susan Willenborg said, ABC 7 Chicago reports. 

"The Labor Board's important ruling gives Chicago families more certainty that the CTU leadership cannot strike illegally whenever they want, and we are gratified that the board has taken a major step toward injunctive relief against future strikes," CPS CEO Forrest Claypool said via statement. 

For its part, the CTU released the following comment in response to the ruling: "The governor's labor board is prosecuting its war on workers. The IELRB's new Rauner-appointed chairwoman, Andrea Waintroob, was the law partner of Chicago Board of Education attorney James Franczek (who argued the Board of Education's case today) until she resigned last April to oversee the IELRB. The IELRB ignored its own precedent and well-established labor law to seek an injunction, in Waintroob's words, to 'send a message' to the Chicago Teachers Union. Former IELRB chairwoman Lynne Sered, who remains on the labor board, dissented and reminded all in attendance that in seeking an injunction against the CTU, the IELRB was ignoring decades of its own legal precedents."