A group launching a legal challenge to Ontario's child vaccination system is planning a rally at the provincial legislature in Toronto today.

The group, which consists of five mothers and the organization Vaccine Choice Canada, is also expected to hold a news conference on its constitutional challenge.

They allege the Immunization of School Pupils Act breaches several charter rights, including those to freedom of conscience and religion as well as liberty and security of the person.

The law requires that children be immunized against certain diseases unless their parents get an objection for medical reasons or over their beliefs.

The Immunization of School Pupils Act requires that children be immunized against certain diseases unless their parents obtain an objection for medical reasons or over their beliefs. (Evan Mitsui/CBC)

To get a non-medical exemption, however, parents must sign a statement of conscience or religious belief and, as of 2017, attend an information session.

Children whose parents don't comply can be suspended from school on order from a medical officer of health.

The allegations have not been tested in court.

A spokesperson for the minister of health says the government can't comment on a case before the courts, but is committed to ensuring a strong and effective immunization system.

Push for more rigid laws

New Brunswick and B.C. also have mandatory vaccination laws for schoolchildren in place.

Dominic Cardy, minister of health in New Brunswick, has pushed for legislation that would eliminate existing religious and philosophical exemptions for unvaccinated children.

Toronto's chief medical officer has similarly advocated for a more restrictive law in Ontario.

In a September report, Dr. Eileen de Villa recommended that the Ontario government consider changing the Immunization of School Pupils Act to only accept medical exemptions from a certified health-care provider.

"Before philosophical and religious exemption rates reach dangerously high levels in Toronto, it is important and timely for the provincial Ministry of Health to consider removing philosophical and religious exemptions from its legislation," de Villa wrote.

In response, Ontario's Ministry of Health said at the time that it had "no plans" to revise the province's approach.