A German cardinal criticised Church leaders who allow divorced and remarried Catholics to take Communion in an interview published Tuesday.

Walter Brandmüller called these priests heretics, and said they are a threat to the unity of the Church.

The cardinal was responding to a proposal by German Cardinal Walter Kasper that remarried Catholics be allowed to take Communion after confessing their sins. The Church currently teaches that only annulled marriages are considered dissolved, and divorced persons who remarry are considered adulterers.

Kasper's proposal has support from some Church leaders, but Brandmüller decried it as blasphemous.

"An adaptation of the moral teaching is not acceptable," he told LifeSite News. "'Do not conform to the world,' said the Apostle St. Paul.

"A change of the teaching, of the dogma, is unthinkable. Who nevertheless consciously does it, or insistently demands it, is a heretic — even if he wears the Roman purple," the cardinal continued.

Other critics of Cardinal Kasper's proposal said that the change would suggest that marriages are not meant to be permanent, and directly contradicts Church teachings.

Last year, Pope Francis said that the Church must welcome divorced Catholics, and criticised the church's prohibitions against them becoming godparents, taking Communion, and reading during Mass.

"It seems they are excommunicated de facto," he told the Argentine newspaper La Nación, suggesting that the church should "open the doors a little bit more." Francis did not address the issue of remarried Catholics receiving communion, but asked "Why can't they be godparents?"

In the same interview, the pontiff said the Church should support families of homosexuals, "(and consider) how can they raise him or her."

Pope Francis has not publicly endorsed Kasper's proposal, which was discussed in a bishop synod on the family lat year.