The liberal justice Sonia Sotomayor has warned that the US supreme court is dismantling the wall between church and state, after the conservative majority ruled that the state of Maine cannot exclude religious schools from a tuition programme.

In a dissent to the ruling in Carson v Makin, released on Tuesday, Sotomayor wrote: “This court continues to dismantle the wall of separation between church and state that the framers fought to build.

“… In just a few years, the court has upended constitutional doctrine, shifting from a rule that permits states to decline to fund religious organisations to one that requires states in many circumstances to subsidise religious indoctrination with taxpayer dollars.”

Progressives fear other rulings due this month, among them a case set to bring down Roe v Wade, the 1973 ruling which established the right to abortion, and a ruling on a New York law set to loosen gun regulations even after several horrific mass shootings.

Supreme court justices often claim not to rule according to political beliefs but few serious observers give such claims any credence.

In the Maine case, John Roberts, the chief justice, wrote for the conservative majority. In Roberts’ view, the tuition programme violated the free exercise clause of the first amendment to the US constitution, because it said private schools were “eligible to receive the payments, so long as they [we]re ‘nonsectarian’”.

Roberts wrote: “Regardless of how the benefit and restriction are described, the programme operates to identify and exclude otherwise eligible schools on the basis of their religious exercise.”

A conservative, Roberts was appointed by George W Bush. Since Republicans rammed three new justices on to the court under Donald Trump, the chief justice has become in some cases a voice for moderation. Not this time.

Sotomayor wrote: “While purporting to protect against discrimination of one kind, the court requires Maine to fund what many of its citizens believe to be discrimination of other kinds.”

The main dissent was written by Stephen Breyer, at 83 the oldest of three liberals on the nine-judge panel. Breyer will soon retire, to be replaced by Ketanji Brown Jackson, Joe Biden’s first pick and the first Black woman confirmed to the court.

Like her fellow liberal Elena Kagan, Sotomayor was nominated by Barack Obama.

Concluding her dissent, Sotomayor wrote: “What a difference five years makes. In 2017, I feared that the court was ‘lead[ing] us … to a place where separation of church and state is a constitutional slogan, not a constitutional commitment’.

“Today, the court leads us to a place where separation of church and state becomes a constitutional violation. If a state cannot offer subsidies to its citizens without being required to fund religious exercise, any state that values its historic antiestablishment interests more than this court does will have to curtail the support it offers to its citizens.

“With growing concern for where this court will lead us next, I respectfully dissent.”

Her words caused a stir. Antony Michael Kreis, a law professor and political scientist at Georgia State University, wrote: “Sotomayor is not having it today.”

Nonetheless, Roberts’ ruling was further evidence of a court in conservatives’ grip.

Last week, addressing progressive lawyers in Washington, Sotomayor said: “There are days I get discouraged. There are moments where I am deeply, deeply disappointed. And yes, there have been moments when I’ve stopped and said, ‘Is this worth it any more?’

“And every time when I do that, I lick my wounds for a while, sometimes I cry, and then I say, ‘OK, let’s fight.’”