Blasphemy of the Holy Spirit is not just about speaking in tongues but IMHO, whenever someone attributes the work of the Holy Spirit to demons ie: OSAS followers attributing obedience to God as an essential part of salvation taught and preached by some on another thread I visited...to demons by saying that "it is not of God".
When Jesus told His disciples to preach the Gospel unto all nations and teach them to obey His commands as written in Matthew 28:19-20, would it be right to call these people malicious and insulting names and saying that their teaching is "not of God, thereby rejecting God's and Jesus' teachings above regarding obedience and attributing them to demons.
I do not speak in tongues but just as Paul said,
NIV1984 1 Corinthians 14:5,18-22,39-40
I would like every one of you to speak in tongues, but I would rather have you prophesy. He who prophesies is greater than one who speaks in tongues, unless he interprets, so that the church may be edified. I thank God that I speak in tongues more than all of you. But in the church I would rather speak five intelligible words to instruct others than ten thousand words in a tongue. Brothers, stop thinking like children. In regard to evil be infants, but in your thinking be adults. In the Law it is written: “Through men of strange tongues and through the lips of foreigners I will speak to this people, but even then they will not listen to me,” says the Lord. Tongues, then, are a sign, not for believers but for unbelievers; prophecy, however, is for believers, not for unbelievers. Therefore, my brothers, be eager to prophesy, and DO NOT FORBID SPEAKING IN TONGUES. But everything should be done in a fitting and orderly way.
If someone was given the gift of tongues and you call it as demonic then you have blasphemed to the Holy Spirit which according to scriptures is unforgivable.
God bless us all.