Universae Ecclesiae released - full English text

[Vetus Ordo]

Wow! I have no idea what you are talking about. I have been to dozens of SSPX chapels and never once have I heard that attendance at the NO was a mortal sin. You are almost certainly making that up, and I consider it a grave detraction of the society. The NO is scandalous and may potentially jeopardize your faith, to be sure, but it is not a mortal sin. Shame on you!

It's certainly a mortal sin for those who know what it is and what it stands for.

A fully informed Christian will not attend a Mass that is sacrilegious and scandalous.