WASHINGTON (Reuters) - Despite wondering every autumn whether she can afford it, Kendra Espinoza has worked hard to keep her two daughters in a small private Christian school in Kalispell, Montana, costing about $15,000 annually for them to attend.

The buliding of the U.S. Supreme Court is pictured in Washington, D.C., U.S., January 19, 2020. REUTERS/Will Dunham

Even with some financial support from the school Espinoza, a single mother, still has a sizable tuition bill to pay. She decided against sending the girls, ages 14 and 11, to local public schools that would be free to attend. On top of her full-time office manager job, Espinoza has worked nights as a janitor in an office building to help pay for tuition, taking her daughters along to instill in them a strong work ethic.

If you want something enough in life, Espinoza said, you have to fight for it.

“The way I try to raise my girls, of course I want them to be able to read the Bible and be taught how to pray, taught from that faith-based perspective,” Espinoza said in an interview. “At the public school, there’s a lot of disrespect and not enough of those values that I wanted them to learn.”

Espinoza, 47, is a plaintiff in a major religious rights case that will be argued before the U.S. Supreme Court on Wednesday. She and two other mothers of students at Stillwater Christian School are appealing a lower court ruling that struck down a Montana state tax credit that could help students pay to attend private schools including religious ones.

A 2015 Montana law provided people a tax credit of up to $150 for donations to groups that fund scholarships for private school tuition. State tax officials limited the program to non-religious schools in order to comport with the state constitution, which forbids public aid to any “church, sect or denomination.” Thirty-eight states have such constitutional provisions.

But the Montana Supreme Court struck down the scholarship program entirely because it could be used to pay for religious schools.

“This is grossly unfair to any parents of kids who go to religious school,” said Espinoza, who is represented by the Institute for Justice, a libertarian legal group. “It’s not fair to us to be excluded (from) funds available to the general public.”

The Supreme Court’s ruling in the case, due by the end of June, could narrow the separation of church and state.

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In their appeal to the nine justices, lawyers for the plaintiffs argued that Montana’s decision to exclude religious school students from the scholarship program violated their rights under the U.S. Constitution to free exercise of religion and equal protection under the law.

It is an argument that could find favor with the court, which has a 5-4 conservative majority.

Under the Montana program, individuals could donate to a scholarship fund organization and receive up to a $150 tax credit. The one scholarship organization that currently exists provides $500 scholarships, primarily to needy students.

Proponents of religious school funding contend that the no-aid to religious institutions provisions in place in 38 states are so-called Blaine amendments, written into the majority of state constitutions in the 19th century as a form of anti-Catholic discrimination.

Montana disagrees, noting that the state adopted a new constitution in 1972 and kept the no-aid provision, believing it would protect religious freedom by preventing the government from gaining influence over religious schools and weakening public schools.

President Donald Trump’s administration is backing the plaintiffs in the case. The Republican president, seeking re-election on Nov. 3, enjoys strong support among evangelical Christian voters. At a rally in Florida this month he pledged to bring prayer to public schools.

Though the plaintiffs are asking the justices to rule in their favor on the tax credit program, Trump’s administration has a broader goal in mind: knocking out state constitution no-aid provisions.

“Because the no-aid provision contravenes the U.S. Constitution, the state court had no authority to enforce it,” Solicitor General Noel Francisco said in a court filing.

Opponents of government support for religion as well as public educators have expressed alarm at the possible ramifications of a ruling in favor of the plaintiffs.

Such a decision could lead to the unprecedented outcome of requiring state funding for religious education or other activities, said Rachel Laser, president of the advocacy group Americans United for Separation of Church and State.

“The question before the court is whether states can continue to protect their citizens’ religious freedom by ensuring that public money not be used to fund religious education and discrimination. The answer must be yes,” Laser said.

Expanding tax credits and vouchers for private education takes scarce resources away from public education, added Lily Eskelsen Garcia, president of the National Education Association, a union that represents public school teachers nationwide.

The case is “an obvious attempt to use the Supreme Court to move this political agenda,” she said.

Eighteen other states have tax-credit programs like the one ended in Montana, supporting around 250,000 students, according to a court filing. Most private schools in those states are religious.

Espinoza’s case could give the justices an opportunity to build on a major 2017 religious rights ruling in favor of a Missouri church that challenged its exclusion from state playground improvement grants generally available to other nonprofit groups. The Supreme Court ruled 7-2 that churches and other religious entities cannot be flatly denied public money even in states where constitutions explicitly ban such funding.

“People will say that they’re afraid of religion being pushed down their throat but I don’t believe that’s an issue in this case,” Espinoza said. “If funds are donated by private citizens to a private organization, just because they have a tax credit attached doesn’t make them public funds.”