In a move that is expected to deepen polarization in Venezuela, the country’s Supreme Court on Tuesday ruled that the opposition-controlled congress had no right to investigate judges who were sworn in at the last minute by the outgoing National Assembly.

In a much-anticipated ruling, the court said the National Assembly’s questioning of the Dec. 23 appointment of 13 judges violated the notion of the separation of powers and constituted a “fraud against the fundamental order.”

When Venezuela’s opposition took control of congress for the first time in 17 years in January, one of its first moves was to create a commission to study the lame-duck appointments.

The opposition claims it has proof that some judges were forced to quit so the ruling party could stack the judiciary with loyalists.

“In general terms, this isn’t a surprise,” National Assembly President Henry Ramos Allup told El Universal newspaper. But he said congress would not behave rashly and that the lengthy ruling “requires a thought-out response.”

The ruling is the latest obstacle for a congress that is struggling to flex its muscles in a country where all other branches of government are controlled by the ruling party.

The court said congress’ role is limited to nominating and appointing judges. And that the only way it can remove magistrates is after an investigation into wrongdoing and with a two-thirds majority vote.

While the opposition did win a two-thirds majority in December’s election, the courts didn’t allow the swearing-in of three of their deputies amid allegations of voter fraud in the state of Amazonas. The opposition has long claimed that was political trickery to undermine its strength.

The institutional head-butting comes as the nation is locked in a deep economic crisis that has President Nicolás Maduro on the ropes. The opposition has been demanding his resignation and formulating plans to cut his term short.

However, control of the courts — including the powerful constitutional court — is likely to keep congress’ plans in check.

Speaking from Brazil on Tuesday, opposition deputy Luis Florido called on the region to activate the Inter-American Democratic Charter.

“We believe there are enough reasons to activate [the charter],” he said, “because the actions of the Supreme Court against the National Assembly constitute a judicial coup that is putting Venezuela’s democracy at risk.”