Efforts to unionize teachers and staff members at Chicago’s largest and most prominent public charter school network is shaping up to be a contentious fight. 

Educators from Noble Network of Charter Schools filed a complaint with the National Labor Relations Board on Friday, alleging that the administration is illegally trying to thwart their efforts. If Noble teachers are successful and unionize, they would create the largest charter school union in the nation.

A group of Noble teachers announced their unionization efforts in March. Noble operates 16 high schools in Chicago, serving more than 11,000 student.

The complaint says that Noble’s non-solicitation clause, which prevents the union from attempting to recruit colleagues, is overly broad and is being strictly enforced. Also, it accuses management of conducting surveillance of union activity.

“We are only asking for the ability to discuss the prospect of unionization,” said teacher Ann Baltzer in a press release. “Management will not even allow us to meet after students have been dismissed, on our own time.”

In response, Noble released a statement saying, “Noble’s leadership has and will continue to respect every Noble teacher’s right to organize or not to organize.”

Sarah Karp is a reporter for WBEZ. Follow her at @sskedreporter or @wbezeducation.