The US Senate will block a vote on any Supreme Court nominee from President Barack Obama, the Republican Majority Leader in the chamber has warned.
Sen Mitch McConnell acknowledged Mr Obama’s right to propose a replacement for Justice Antonin Scalia, who died earlier this month.
But he stressed that Republicans controlling the Senate would also exercise their rights.
Scalia’s death left the conservative-run Supreme Court evenly divided.
It also set off a battle in a presidential election year over Scalia’s successor into the nine-member body.
“Presidents have a right to nominate, just as the Senate has its constitutional right to provide or withhold consent. In this case, the Senate will withhold it,” Sen McConnell said on Tuesday.
“The Senate will appropriately revisit the matter after the American people finish making in November the decision they’ve already started making today,” he added, in a reference to the 8 November presidential elections.
Meanwhile, the Democrat Minority Leader of the Senate, Harry Reid, described Sen McConnell’s stance on the issue as “obstruction on steroids”.
“Gone are the days of level-headedness and compromise,” Mr Reid said.
The White House said shortly after Scalia’s death that a new judge would soon be nominated by Mr Obama.
Republicans say President Barack Obama should leave this to his successor next year.
According to the constitution, the president nominates justices to the court while the Senate uses its “advice and consent” powers to confirm or reject that person.
Scalia, 79, was found dead at a Texan ranch. He had died of natural causes.
The death of a powerful conservative voice on the bench of the country’s highest court threatens to spark a constitutional crisis in the US.
In recent years, the court has made key rulings on gay marriage, abortion and Mr Obama’s key healthcare legislation.