It calls on the province to double their pay, to almost $200,000 per year, close to what a family doctor makes.
All but one of the province's 682 midwives are women and the Association of Ontario Midwives claims its members are paying a "gender penalty."
"We believe because it's predominantly women providing care to women in a women's health experience [the work] is not as valued by the government," president Lisa Weston told CBC News.
"We've been unable to get the government to live up to its own laws on pay equity."
As independent contractors, midwives are not covered by the province's pay equity legislation, which is why the group is instead framing its claim as a human rights issue.
"I'm protected under human rights legislation whether I'm an employee, a contractor or nobody at all," said Weston.
The lack of male midwives makes it hard to work out whether, as women, they are being underpaid. So the group brought in a pay equity expert who compared the skills, responsibilities and working conditions of midwives to those of occupations that include more men.