Eager for political payback, Senate Democrats plan to do everything they can to block President Trump’s nomination for the Supreme Court — even though they don’t know who it will be.

Sen. Jeff Merkley (D-Ore.) said Monday that he will filibuster any pick that is not Merrick Garland — former President Obama’s nominee to replace the late Antonin Scalia — who was never granted a hearing or a vote by the GOP-controlled Senate.

“This is a stolen seat. This is the first time a Senate majority has stolen a seat. We will use every lever in our power to stop this,” Merkley told Politico, adding that an overwhelming majority of his Democratic caucus will oppose Trump’s pick.

A filibuster would mean that Trump’s nominee — whom he plans to announce on live TV Tuesday evening — will need 60 votes to be confirmed by the Senate.

White House spokesman Sean Spicer later slammed Democrats for their blanket opposition.

“As you know, tomorrow at 8 p.m. the president will announce who he intends to nominate for the Supreme Court. And for a party preaching tolerance, it’s interesting to see some Democrats have already come out against this unnamed individual,” Spicer said, referring to Democrats’ protests over Trump’s radical new immigration policies.

“Before they have even heard who this individual is, you have got some of them saying absolutely no. That just shows you that it’s all about politics. The president has a right to have his nominees taken up. I think that’s a sad message.”

Another Democrat, Amy Klobuchar of Minnesota, tweeted Sunday night that a Senate minority can block Supreme Court nominees.

“Remember this week when Supreme Ct nominee is announced, vote threshold is SIXTY votes, different from the 51 vote margin w/other nominees,” she wrote.

Sen. Chuck Schumer is also on record saying he will fight “tooth and nail” a nominee who isn’t “mainstream.”

The only other top-court filibuster in modern history is when Democrats — including then-Sen. Barack Obama — tried to block President George W. Bush’s nomination of Samuel Alito.

The new fight could lead to a change in Senate rules if the GOP votes to end filibusters, something each party has threatened in the past.

Trump said Monday at the White House he would name “a person who is unbelievably highly respected.”

Three US appeals court judges appointed by Bush are among those under consideration for the high court.

They are: Neil Gorsuch, a judge on the Denver-based 10th US Circuit Court of Appeals; Thomas Hardiman, who serves on the Philadelphia-based 3rd US Circuit Court of Appeals; and William Pryor, a judge on the Atlanta-based 11th US Circuit Court of Appeals.

Since Scalia’s death, the Supreme Court has been ideologically split, with four conservatives and four liberals on the bench.

Another conservative justice could be pivotal in cases involving abortions; gun, religious and transgender rights; the death penalty, and other contentious issues.

Democrats remain furious over Senate Majority Leader Mitch McConnell’s refusal last year to allow the Senate to consider Obama’s nomination of Garland for the vacant seat, an action with little precedent in US history.

Trump, who took office Jan. 20, said last week that evangelical Christians “will love my pick.”

Gorsuch, Hardiman and Pryor all possess strong conservative credentials.