A work-to-rule campaign by unionized transit workers in Calgary forced the cancellation Tuesday of nearly 20 buses across the city serving high school students.

While most schools lost one or two buses, William Aberhart high school in the northwest lost four buses.

Grade 11 student Corey Eaton got a ride to school Tuesday after his bus was cancelled. 

"For my mom, it's a big pain. She has to drive us to school," Eaton said. "It's about a 15, 20 minute drive."

The public school board contracts city buses to exclusively carry students to and from school.

But the union representing Calgary's transit workers began a work-to-rule campaign Friday morning, refusing to work voluntary overtime.

The Amalgamated Transit Union Local 583, which has been without a contract since June, represents 2,400 workers, including bus drivers, C-Train operators and office and maintenance staff.

Parent Wam Boa had to rearrange his schedule to drive his son to Aberhart.

"It's going to set me back right through the day now because I'm supposed to be at work right now," he said Tuesday morning. "I'll have to find a way to get back here again to come and pick him up."

Despite the inconvenience, Boa said he supports the transit workers in their efforts to get a new contract.