That would mean their teachings, being sin, would be unforgivable. I don't know if they are guilty of that. Some may be, some may not. It would fit.
Jud 1:3 Beloved, while I was making every effort to write you about our common salvation, I felt the necessity to write to you appealing that you contend earnestly for the faith which was once for all handed down to the saints.
Jud 1:4 For certain persons have crept in unnoticed, those who were long beforehand marked out for this condemnation, ungodly persons who turn the grace of our God into licentiousness and deny our only Master and Lord, Jesus Christ. (NASB, emphasis mine)