WASHINGTON (NewsNation Now) — Congressional Democrats plan to introduce legislation on Thursday to expand the U.S. Supreme Court by four justices, expanding the number of justices from the current nine to 13, according to a copy of the Senate bill reviewed by Reuters.

President Joe Biden announced last Friday the formation of a bipartisan commission to study potential Supreme Court changes including expansion or imposing term limits on the justices instead of the current lifetime appointments.

The conversation around expanding the court grew during the 2020 election when candidates like Massachusetts Senator Elizabeth Warren and Transportation Secretary Pete Buttigieg supported raising the number of justices on the bench.

“It’s not just about expansion, it’s about depoliticizing the Supreme Court,” Warren told Politico at the time.

The confirmation of Justice Amy Coney Barrett also created calls for “court packing;” Democrats viewed her appointment as unfair due to the timing of Barrett’s late October 2020 confirmation.

Republicans have voiced strong opposition in the past to the idea of expanding the bench, with it becoming an attack against then-candidates Biden and Kamala Harris.

During the 2020 Vice Presidential debate, former Vice President Mike Pence said “the straight answer is they are going to pack the Supreme Court if they somehow win this election.”

WHY DOES THE U.S. SUPREME COURT HAVE NINE JUSTICES?

The U.S. Constitution places the power to determine the number of justices on the Supreme Court in the hands of Congress. All justices appointed to the lifetime role are nominated by the president and confirmed by the Senate.

It’s under Congress’ direction to establish courts, according to Article 3, Section 1.

The Judiciary Act of 1789 set the number of justices at six — one chief justice and five associates.

Since then, Congress has passed various legislation to change the number of justices on the high court, which has fluctuated from a low of five to a high of 10.

The Judiciary Act of 1869 fixed the number of justices at nine. No subsequent change to the number of justices on the U.S. Supreme Court has occurred since.

WHEN WAS THE LAST TIME A PRESIDENT TRIED TO CHANGE THE SIZE OF THE HIGH COURT?

Franklin D. Roosevelt was the last president who attempted to expand the Supreme Court’s membership. After winning the 1936 presidential election, Roosevelt proposed a bill that would have added one justice to the court for each justice over the age of 70, with a maximum cap of six.

However, Roosevelt received backlash over the legislation, and it was never enacted by Congress.

HOW MANY JUSTICES MUST BE PRESENT TO HEAR A CASE?

A quorum of six justices is needed in order to decide a case, according to the Supreme Court. Justices can participate by listening to audio recordings of the oral arguments, as well as by reading transcripts.

Reuters contributed to this report.