Pope Francis has warned US Catholic bishops not to deny Joe Biden communion when he attends his weekly Mass.

The Pope's warning came via a letter from Cardinal Luis Ladaria, prefect of the Vatican's Congregation for the Doctrine of the Faith, addressed to Archbishop José Gomez of Los Angeles, president of the US Conference of Catholic Bishops (USCCB).

Any new policy "requires that dialogue occurs in two stages: first among the bishops themselves, and then between bishops and Catholic pro-choice politicians within their jurisdictions," the letter said.

It also laid out liberal guidelines for dealing with politicians who support reproductive choice.

The bishops are scheduled to meet June 16 through 18, and the proposal to formally bar the president from taking communion is on their agenda.

According to the New York Times, the proposal is being pushed by notoriously conservative Archbishop Salvatore Cordileone of San Francisco. Among the complaints against Biden is his support for reproductive choice and marriage equality — both of which Cordileone abhors.

Biden, the first Roman Catholic to occupy the White House since John F. Kennedy, is a devout Catholic who attends Mass every Sunday.

He has previously been denied communion by priests acting on their own authority. A vote by the USCCB would add an extra layer of authority to the ban.

Holy Communion is an important sacrament in the Catholic Church, because it is believed to be the actual body and blood of Christ. Receiving it represents an individual's oneness with Christ and the Church.

Biden is not the only politician to be denied communion by priests — although he would be the first one to be barred by a vote of the USCCB, if that occurs.

Sen. Ted Kennedy and New York Gov. Andrew Cuomo have also been barred from communion, and for similar reasons. Like them, Biden has simply sought out friendly priests to administer the sacrament.

John Kelley, the Biden staffer who was in charge of finding those friendly priests for Biden during his 2008 campaign for vice president, told the Washington Post that taking part in worship led by local priests is important to Biden, and doing so in public, not tucked away in a private Mass, is vital to him.

"They felt, and they were right, that he wants to go to church and should have the right to. He wants to worship with his community. His understanding of the Eucharist was it shouldn't be done hidden in private. I very much felt the Eucharist was being weaponized," Kelly said.

Hardline conservative clergy seem determined not to compromise on this issue, however.

"Holy Communion signifies we are one with God, each other, and the Church. Our actions should reflect that," said Reverend Robert E. Morey, a priest in Florence, SC, who actually refused to give Biden communion in 2019.

Bishops, perhaps more attuned to the political implications of denying sacraments to a sitting US president, have been more circumspect.

"Because President Biden is Catholic, it presents a unique problem for us," Archbishop Joseph Naumann of Kansas City told the Associated Press.

"It can create confusion... How can he say he's a devout Catholic and he's doing these things that are contrary to the church's teaching?"

According to a March 2021 Pew Research Centre poll, 67% of Catholics think Biden should be allowed to receive communion. However, 55% of Republican Catholics wanted to bar him from the sacrament.

According to the New York Times, there are 280 voting bishops sitting on the US Conference of Catholic Bishops.

Seventy of them have written to Archbishop Gomez, urging him to postpone the vote until they can meet in person for more discussion. However, this was rejected, and the USCCB is reportedly pushing on to vote on Cordileone's proposal.