A coalition of Congressional Democrats will introduce legislation that would pack the Supreme Court with four more justices, a move that would tilt the ideological advantage towards liberals, who now suffer a 3-6 minority.

While unlikely to pass, the proposal is the latest salvo in the most serious effort to expand the number of Supreme Court justices (from 9 to 13) since the Franklin Delano Roosevelt administration.

President Biden has resisted pressure from some progressives to dilute the conservative majority. Last week, he formed a commission to study the issue, which many Washington-watchers identified as a way to ignore it. Biden has said he is “not a fan” of adding seats to the Supreme Court.

Likewise, progressive standard-bearer Bernie Sanders, the independent Senator from Vermont, has warned that tinkering with the size of the court can lead to a tit-for-tat partisan battle. “My worry is that the next time the Republicans are in power they will do the same thing,” Sanders has said.

NBC News notes that the effort to reform the court is a reaction to the perception that Republicans have comprised it:

…it represents an undercurrent of progressive fury at Senate Minority Leader Mitch McConnell, R-Ky., for denying a vote in 2016 to President Barack Obama’s pick to fill a vacancy, citing the approaching election, before confirming Trump nominee Amy Coney Barrett the week before the election last year.

Sen. Ed Markey of Massachusetts and Rep. Jerry Nadler of New York are co-sponsors of the forthcoming bill.

The size of the Supreme Court has fluctuated since it was established in 1789. But it has remained at nine for over a 150 years.