A group of pregnant Canadian women launched a class-action lawsuit Friday against the maker of a recalled birth control pill after it was discovered the packages contained mostly placebos.

The lawsuit over 45 unwanted pregnancies and four abortions seeks Can$800 million (US$778.8 million) against pharmaceutical firm Apotex, the maker of the birth control pill Alysena.

"When they first got the news that they were pregnant they were shocked, stressed out and very worried," lawyer Sandy Zaitzeff said of his clients.

"Raising a child today costs millions of dollars," he told AFP. "In this modern world, people enter into relationships and don't necessarily want to have a child and so should not be burdened with the costs of raising a child."

Thousands of pill packages with the lot number LF01899A were recalled April 8 because some packages contained two weeks worth of placebo pills instead of just one.

Days later, the recall was expanded to 11 other lots, for a total of 550,000 packages.

Health Minister Leona Aglukkaq has ordered an investigation into a five-day delay in informing the public.