Supporters of the proposal plan to hold a news conference on the steps of the Supreme Court building. They include U.S. Sen. Ed Markey of Massachusetts and U.S. Reps. Jerry Nadler and Mondaire Jones, both of New York, and Hank Johnson of Georgia.
Given Democrats' control of the White House and Senate, the legislation could allow the party to supersede the court's current conservative majority by "packing" the Court with liberal justices.
Some Republicans quickly derided the proposal.
"Does expanding the Supreme Court count as infrastructure too?" Rep. Jim Jordan, R-Ohio, wrote on Twitter.
Jones responded simply: "Yes," with a heart emoji.
"Imagine if we reduced the number from nine to five and just kept the Republicans. You guys would go crazy," Jordan added, according to the Washington Times.
Rep. Mike Johnson, R-La., also criticized the court plan in a proposed amendment for a bill addressing possible reparations for African-Americans, the outlet reported.
"The idea of packing the Supreme Court is so dangerous, we have to address it now," Johnson wrote.
Spokespeople for the Democratic backers of the proposal did not respond Wednesday night to Fox News’ requests for further details.
The legislation will propose expanding the court to 13 justices, from nine, The Intercept reported Wednesday.
The Supreme Court has had nine justices since the 19th century, though the number of justices is not specified in the Constitution.
Earlier this year, Sen. Ted Cruz, R-Texas, introduced legislation calling for a constitutional amendment to preserve the current number of sitting justices, as well as provisions prohibiting Congress from passing legislation to expand the number.
Cruz previously introduced his plan last October, as some Democrats indicated an openness to expanding the size of the high court following the Sept. 18 death of Justice Ruth Bader Ginsburg.
The court vacancy created by Ginsburg's death was ultimately filled by Amy Coney Barrett, who became then-President Trump’s third appointment to the Supreme Court.
Barrett was expected to tilt the ideological power balance of the court in favor of conservatives, 6 to 3 -- although Chief Justice John Roberts and Trump-appointed justices Brett Kavanaugh and Neil Gorsuch have at times sided with the court's liberals.
Democrats often attribute part of the shift in the court to the fact that then-Sen. Majority Leader Mitch McConnell, R-Ky., refused to consider Merrick Garland – nominated by President Barack Obama in 2016 – to fill a vacant seat during an election year. That seat, belonging to Antonin Scalia, eventually went to Gorsuch.
Following the Garland situation, Sen. Elizabeth Warren, D-Mass., said "every option" needed to be on the table to restore credibility and integrity to the Supreme Court.
Rep. Alexandria Ocasio-Cortez, D-N.Y., in October tweeted, "expand the court."
President Biden has previously opposed the idea of court-packing. However, he said in the fall that he intended to set up a bipartisan commission to study Supreme Court reforms.
This week, Biden signed an executive order forming the "Presidential Commission on the Supreme Court of the United States" to analyze the merits of proposed reforms.