After three days of job action by Ontario high-school teachers, at least one official is saying student safety has been the first casualty.

Ken Arnott, president of the Ontario Principals' Council, said some of his colleagues across the province are voicing concerns over the recent work-to-rule strike.

In one case, Arnott said 1,000 students were being supervised by a single administrator. In another, nine educational assistants who supervise students as they arrive and leave school are no longer doing their jobs, meaning administrators have to pick up the slack.

"They're not as safe as they would be under normal circumstances," he said, declining to name specific schools where concerns were reported.

The Ontario Secondary School Teachers' Federation is locked in a standoff with the province over a new contract. Bill 115, which was passed in September, places a two-year wage freeze on veteran teachers and limits the ability to bank sick days. The law also targets collective bargaining rights, giving the province the power to ban lockouts and strikes.

On Monday, teachers from 20 OSSTF boards -- including Toronto, Halton and Durham -- stopped doing certain administrative duties as part of an effort to spark some movement on the negotiating front.

While teachers are still performing their classroom duties, those in Ontario’s high schools are no longer suprvising students during breaks or communicating with parents outside of school hours, among other service withdrawals. And while secondary teachers are filling out report cards, they are not entering them into the system, causing some delays.

Arnott told CTV News student safety is being compromised as a result of such job action.

"We've been gathering information from principals all across the province," he said. "There are principals who are out of the office a lot more than usual, dealing with attendance and on-call issues, and therefore not available to deal with some of the things coming into the office."

But it’s more than the staff getting frustrated.

Arnott said he's heard reports in a number of schools that students are becoming angry at the lack of services -- such as gym supervision during free hours. In some cases, students taking advantage of the situation to act out, while others are considering holding walkouts in protest.

He said principals and other administrators are doing what they can, but said safety is "not adequate" at this point.

For its part, the Trillium Lakeland District School Board said Wednesday it would lock out teachers if it feels students are in danger. School Board Chair Karen Round said trustees have given senior administrators the authority to lock out Trillium teachers if they deem students to be at risk.

It's unclear how long the job action will continue as no further talks between the two sides are scheduled.

OSSTF has said it will continue the job action until the province shows signs that it is serious about hammering out a deal.

Meanwhile, elementary teachers in some boards are expected to begin "escalating" job action on Monday.

For now, they have been told by their union to fill out student report cards, but only with a bare minimum of information. Some principals have refused to send those report cards home with students, deeming them to be incomplete.