Venezuela’s Supreme Court has consolidated President Nicolás Maduro’s power with a decision that removes budgetary authority from the nation’s Congress, the only institution that is controlled by the opposition.

The ruling late Tuesday came as opponents of the president prepared to gather enough signatures for a recall referendum to force him from office.

The judges’ decision allows the court itself to approve Mr. Maduro’s budget, which he is expected to present by decree on Friday. The move caps a yearlong effort by the leftist government to use the courts, which are controlled by Maduro loyalists, to neutralize the Congress.

It could also forecast a more aggressive campaign by Mr. Maduro to derail the recall referendum.

Mr. Maduro came to power in 2013 upon the death of Hugo Chávez, the charismatic former army officer who founded Venezuela’s populist, leftist movement. But after Mr. Maduro’s own election three years ago, the price of oil, which had financed Mr. Chávez’s many ambitious programs, went into a global tailspin.