The incident happened Thursday at St. Patrick High School in the northern city of Thunder Bay when Alexandria Szeglet was sent home for the day, the Globe and Mail reported.
Some students were participating in a Day of Silent Solidarity fundraising effort for a school anti-abortion group and were wearing "pro-life" anti-abortion messages made form red tape on their uniforms. The project had been approved by the school.
Szeglet substituted "choice" for life on her own uniform in green tape and was sent home, the report said.
Friday, 24 other students backed Szeglet with similar "choice" messages and four of them were sent home.
John De Faveri, director of education with the Thunder Bay Catholic District School Board, told the newspaper it wasn't the message but how it was conveyed.
"It wasn't anything about what the students were trying to say. It was the inappropriate way they went about it," he said. "They didn't get approval from the school."
Ann Szeglet, Alexandria's mother, told the Globe it seemed religion had trumped democracy.
"My opinion is that if they don't want to allow both sides to express their opinion. They shouldn't allow either one of them," she said.