The Philippine Supreme Court has struck down a legal challenge to a controversial birth control law that supporters say could transform the lives of millions of poor Filipinos, despite bitter opposition from the country's powerful Roman Catholic Church.

"The RH law is not unconstitutional," Supreme Court spokesman Theodore Te told reporters on Tuesday, announcing the ruling denying the petitions to the law filed by church groups.

The law requires the government to provide free contraception to the poorest Filipinos, and conduct safe sex education in schools.

"This monumental decision upholds the separation of church and state and affirms the supremacy of government in secular concerns like health and socio-economic development," said Edcel Lagman, a congressman and the principal author of the law.

The debate over the constitutionality of the law, which was signed by President Benigno Aquino in 2012, pits the government against the church in a country where at least 80 percent of the population are Roman Catholics.

The latest survey shows that 72 percent of the Philippine population supports the law.

For more than a decade, politicians have tried to pass the law, but were repeatedly blocked by the church.

Stemming population growth

Supporters say the law is necessary to stem population growth, reduce maternal death rates and help avoid unwanted pregnancies among poor women. They also contend that it could help slow down the spread of sexually-transmitted diseases, including HIV-AIDS, which saw sharp increases over the past five years.

The Philippine population has also tripled since 1970, and is expected to officially hit 100 million by 2014.

The population growth in the Philippines is one of the fastest growing in the world, but opponents argue that the growth rate is actually slowing down, in line with many other countries.

Some church leaders are urging people not to use contraceptives, even if they are given to them for free, saying they have a moral responsibility to have the law overturned.

Father Melvin Castro, of the Catholic Bishops Conference of the Philippines, said contraceptives were not the answer to poverty. "They are poor not because they have no access to contraceptives but because they have no work. Give them work and it will be the most effective birth spacing means for them."

Another concern in the Philippines is the number of women dying during childbirth. The latest family health survey estimated a 36 percent rise in 2011 in the maternal mortality rate, to 221 per 100,000 live births.

One of the hardline opponents of the legislation and a petitioner to the court, former senator Francisco Tatad, said allowing the law to take effect could force Catholics into an open revolt.

"Some of us will want to defy the power of the devil and die as martyrs, if need be, in the only cause that gives us a chance to fight for something much bigger than ourselves."