A law firm is preparing a class action for about 100 women who say they were forced to give up their babies during the 1960s and 70s.

Porters Lawyers, a Canberra-based firm, is representing the women who claim they were forced to give up their babies at a number of institutions and hospitals run by charities and church orders around Australia.

They include about a dozen women in Western Australia who claim their babies were taken away from them by the Catholic Church order of Sisters of Mercy.