I appreciate the response. As for Biblical authority Matthew 16:18-19 gives the Holy Roman Catholic Church all the authority it needs to decide such matters, particularly when it comes to administering the sacraments.
As such The Church’s Canon No.: 915 states: Those upon whom the penalty of excommunication or interdict has been imposed or declared, and others who obstinately persist in manifest grave sin, are not to be admitted to holy communion.
Furthermore as 1 Corinthians 11:27 tells us that those who eat the Body and Blood of Christ do so unworthily and furher condemn themselves.
Therefore, denying someone who is in a state of manifest grave sin is the duty of the priest. It is also an act of mercy to prevent further damnation of the individual’s soul.
Matthew 16:18-19 does not expressly give anyone authority to prevent one from communion. It's a statement that "upon this rock will I build my church." It is not a blank check to any man.
1 Corinthians 11:27 warns believers but does not expressly forbid believers from taking communion.
Don't want to keep on this I don't think because the basic Catholic tenants of those two verses, misinterpreted IMO, has been debated for centuries. Nevertheless, even if you grant the Catholic version of Mat 16:18-19, that does not necessarily presume all acts by the Pope are of God nor justify unscriptural acts.
My thoughts, but we'll never solve that part of things here. However, I hope I've helped someone who may be watching.