By a simple comparison between their doctrine and practices on this issue with the Bible.

No women speaking in tongues or prophesying - yet the tongues movement is filled with women preachers and tongues-speakers.

Only two or three speaking in one meeting, and taking turns, plus an interpretor or else they must be silent. Yet, I have seen whole churches doing this at one, no interpretor.

The teaching that all should speak in tongues - when the Bible indicates that God did NOT give the gift to all. Plus, the teaching that it is the evidence of being saved and/or being filled with the Spirit of God - which does not line up with the Bible.

The Bible also teaches it is the least of the gifts - yet charismatics and pentecostals want to make it the greatest.

The gifts were given to to edify the church - yet many teach that you can have a private prayer tongue language (which the Bible does not teach anywhere).

As has already been pointed out, tongues were a sign to lost Jews - yet we see many churches filled with Gentiles only who practice this.