A union-free school district is a school district in which the school employees (teachers, teachers aides, clerical employees, support staff etc.) are not represented by a labor union. This means that the wages, hours of work, and conditions of employment, including academic freedom (or the lack of it) are at the sole discretion of the employer and can be changed by the School District Administration as it deems necessary. The only limitations on this latitude are laws or regulations that may exist in State Education Codes and state or federal civil rights laws. Schools are exempt from federal wage and hour laws, so overtime in schools is not regulated.
The above is entirely incorrect. A union free school district has absolutely nothing to do with labor unions. According to the NY State Department of Education:
<<A union free school district is a school district generally formed from one or more common school districts to operate a high school program, which common school districts cannot do. First authorized by legislation in 1853, union free school districts are administered by a school board of between three and nine members. The number of members of the board of education of a union free school district may be increased or decreased as set forth in law. Currently, not all union free school districts operate a secondary school program, and some have been established solely as special act school districts to serve children who reside in specified childcare institutions