A CATHOLIC couple has asked the Philippines' top court to stop a historic birth control law, their lawyer said Thursday, in the first of many legal challenges church leaders have vowed against the measure.

The petition was filed Wednesday at the Supreme Court by lawyer James Imbong and his wife, who claim the law signed by President Benigno Aquino 3rd two weeks ago was unconstitutional.

Imbong's mother Jo, who is representing the couple in the case and is the lawyer for the influential Catholic Bishops Conference of the Philippines, told Agence France-Presse that "the state has no business entering the bedroom".

"This law corrupts Philippine culture, mainly the emphasis we put on family values and marriage, taking care of children and parenting," she said, having earlier warned that lay Catholics would challenge the law in court.

The Philippine constitution guaranteed the protection of the family and in passing the law "the government overstepped its powers," Jo Imbong said.

"This is just the first salvo," she added. "We are paving the way for other similar suits from many faith-based groups."

Imbong said that big "prayer rallies" were also being planned across the country in the weeks to come.

The law will take effect on January 17, unless the Supreme Court issues an injunction. Court officials have not indicated if they will hear legal challenges to the law before then.

The law requires government health centers hand out free condoms and birth-control pills, benefiting tens of millions of the country's poor who would not otherwise be able to afford or have access to them.

It also mandates that sex education be taught in schools and public health workers receive family-planning training.

Proponents have said the law will slow the country's rapid population growth, cut poverty and reduce the number of mothers dying at child birth.

The Catholic Church had managed to stall the legislation for more than a decade, cowing legislators and presidents by threatening to turn the public against them.

Eighty percent of the country's roughly 100 million people are Catholic, and the church helped lead "people power" revolutions that toppled two corrupt presidents over the past 27 years.

Nevertheless, public opinion surveys have consistently shown a majority of Filipinos support the "Responsible Parenthood Act."