Heidelberg Catechism · 1563

Q82. Are those also to be admitted to the Lord's supper who by their confession and life show that they are unbelieving and ungodly?

No, for then the covenant of God would be profaned and His wrath kindled against the whole congregation. Therefore, according to the command of Christ and His apostles, the Christian church is duty-bound to exclude such persons by the keys of the kingdom of heaven, until they amend their lives.
Answer · Heidelberg Catechism

Scripture proofs

  1. [1]
    Psalms 50:16

    But unto the wicked God saith, What hast thou to do to declare my statutes, or that thou shouldest take my covenant in thy mouth?

    Isaiah 1:11-17

    To what purpose is the multitude of your sacrifices unto me? saith the Lord: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats. When ye come to appear before me, who hath required this at your hand, to tread my courts? Bring no more vain oblations; incense is an abomination unto me; the new moons and sabbaths, the calling of assemblies, I cannot away with; it is iniquity, even the solemn meeting. …

    1 Corinthians 11:17-34

    Now in this that I declare unto you I praise you not, that ye come together not for the better, but for the worse. For first of all, when ye come together in the church, I hear that there be divisions among you; and I partly believe it. For there must be also heresies among you, that they which are approved may be made manifest among you. …

Proof texts as given in the original; verse text from the King James Version.