WASHINGTON (Reuters) - A California law that requires Christian-based facilities that steer pregnant women away from abortion to post notices about the availability of state-subsidized abortions ran into trouble at the U.S. Supreme Court on Tuesday, with justices on the right and left indicating it may violate free speech rights.

Various justices voiced concern that the Democratic-backed 2015 law was crafted to take aim at a specific viewpoint -- opposition to abortion -- held by these non-profit facilities called crisis pregnancy centers.

Conservative justices sharply questioned the lawyer representing California, and even two liberal justices expressed unease with parts of the law during an hour-long argument in an appeal by these facilities of a lower court ruling upholding the statute. The court has a 5-4 conservative majority.

The crisis pregnancy centers accuse California of compelling them to advertise for abortion even though it violates their beliefs, running afoul of the guarantee of freedom of speech under the U.S. Constitution’s First Amendment.

Conservative Justice Samuel Alito said that even if the law looks neutral on its face, it contains so many exemptions that it appears to target only those holding anti-abortion views.

“Do you think it’s possible to infer intentional discrimination?” Alito asked Joshua Klein, California’s deputy solicitor general.

Liberal Justice Elena Kagan pressed Klein on the same concerns, wondering whether the law was applied only to “speakers whose speech we don’t much like.” Klein said the law was applied to be useful to pregnant women.

California’s Reproductive FACT Act, passed by a Democratic-led legislature and signed by Democratic Governor Jerry Brown, requires centers licensed as family planning facilities to post or distribute notices that the state has programs offering free or low-cost birth control and abortion services. It also requires unlicensed facilities that may have no medical provider on staff to disclose that fact.

The Supreme Court legalized abortion in 1973, and the wider issue of abortion rights is not at issue in the case.

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Crisis pregnancy centers say they offer legitimate health services but that it is their mission to steer women with unplanned pregnancies away from abortion. California says some crisis pregnancy centers mislead women by presenting themselves as full-service reproductive healthcare facilities and the law helps ensure clients are made aware of abortion services available elsewhere.

The San Francisco-based 9th U.S. Circuit Court of Appeals upheld the law in 2016, finding it did not discriminate based on viewpoint.

‘CHOOSE LIFE’

Conservative Justice Anthony Kennedy suggested that if the statute required unlicensed centers to add the disclosure about having no medical provider to a billboard that simply stated “Choose Life” - a slogan for people who oppose abortion - it would violate the Constitution.

Liberal Justice Sonia Sotomayor agreed that such an advertising requirement would be wrong.

Some of the questions from liberal justices suggested they had one eye on future cases in which conservative states pass laws imposing restrictions on abortion clinics.

Liberal Justice Stephen Breyer expressed concern over setting a legal standard that would be seen to favor one side of the abortion debate over the other. Any sort of disclosure law should apply equally whether passed in a state that supports abortion rights or in one that tries to limit them, Breyer said.

If a “pro-life state can tell a doctor you have to tell people about adoption, why can’t a pro-choice state tell a doctor, a facility ... you have to tell people about abortion?” Breyer asked Michael Farris, an attorney with the Alliance Defending Freedom conservative legal group representing the crisis pregnancy centers.

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“What is sauce for the goose is sauce for the gander,” Breyer said.

Farris said while doctors performing medical interventions like abortion can be legally required to discuss the benefits or risks of the procedures, those who merely talk about abortion need not be held to same standard.

“We should not politicize the practice of medicine in that way,” Farris said.

Abortion rights advocates say the roughly 2,700 U.S. anti-abortion pregnancy centers, including around 200 in California, far outnumber facilities providing abortions.

The California challengers are the National Institute of Family and Life Advocates, an umbrella group for crisis pregnancy centers, and two such facilities in San Diego County.

California told the justices in legal papers that some centers use incomplete or false medical advice to try to prevent women from having an abortion. Some resemble medical clinics, down to lab coats worn by staff, to try to confuse women into thinking they are at a facility offering all options, the state added. The facilities deny using deceptive tactics.

A ruling is due by the end of June.