It is specifically forbidden in the Old Testament, there are no positive examples of it being practiced in Scripture, and its origin is clear: it is pagan.
9When thou art come into the land which the LORD thy God giveth thee, thou shalt not learn to do after the abominations of those nations. 10There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch, 11Or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer. 12For all that do these things are an abomination unto the LORD: and because of these abominations the LORD thy God doth drive them out from before thee.
You can feel free to consult with, ask for the intercessions of, and seek the help of those who are living, but communication with the departed is explicitly forbidden and is identified by Scripture as one of the reasons for which the Canaanites were condemned to the punishment of genocide.
This post is by reader request, but to the Glory of God the Father, and His risen Son!
But the "dead in Christ" are alive, therefore we can communicate with them.
The "dead in Christ" are not physically alive, and it is communicating with the physically dead that is prohibited in Scripture. If communicating with the spiritually dead were what is forbidden, we could not evangelize.
Praying to the saints and Mary are found in the Apocryphal books.
Tobit mentions prayers OF the saints.
2 Maccabees mentions praying FOR the dead, but not praying TO the dead.
Baruch also mentions praying FOR the dead, but not praying TO the dead.
Wisdom mocks prayers TO the dead (more specifically, of course, to dead idols):
17Then maketh he prayer for his goods, for his wife and children, and is not ashamed to speak to that which hath no life. 18For health he calleth upon that which is weak: for life prayeth to that which is dead; for aid humbly beseecheth that which hath least means to help: and for a good journey he asketh of that which cannot set a foot forward:
I don't recall any passage of the accepted Apocrypha that mentions praying to anyone but God. Perhaps this objector has confused prayers FOR the dead with prayers TO the dead? Both are wrong, but while some passages of the Apocrypha may be taken to support the former, surely none can be used to support the latter.