Ezra 2:62
They made search for their record among the lists of families, but their names were nowhere to be seen; so they were looked on as unclean and no longer priests.
Numbers 3:10
And give orders that Aaron and his sons are to keep their place as priests; any strange person who comes near is to be put to death.
Leviticus 21:21-23
No man of the offspring of Aaron whose body is damaged in any way may come near to give the fire offerings of the Lord: he is damaged, he may not come near to make the offerings.
Numbers 16:39-40
So Eleazar the priest took the brass vessels which had been offered by those who were burned up, and they were hammered out to make a cover for the altar:
Numbers 18:7
And you and your sons with you are to be responsible as priests for the altar and everything on it, and everything inside the veil; you are to do the work of priests; I have given you your position as priests; and any other man who comes near will be put to death.
Ezekiel 44:10-14
But as for the Levites, who went far from me, when Israel went out of the right way, turning away from me to go after their images; their punishment will come on them.