The union representing teachers at a Hamilton high school is raising concerns about what they believe is a “disproportional amount” of staff who have been diagnosed with cancer.

The chair of the city’s school board says officials take this concern seriously and are taking action.

The local Catholic secondary school teachers’ union said its members are worried about how the school site could be contributing to the number of cases of cancer among staff since 1995 — which they say is 21.

The union says Cathedral High School was built on an old Hamilton Street Railway site that was “contaminated” by an old transformer that remains underground.