Fr. Scott..

http://www.sspx.org/Catholic_FAQs/catholic_faqs__canonical.htm#thucline

However, even were there no doubt at all as to validity, it would still not be permissible to assist at the Masses and receive the sacraments from priests of the Thuc line. For they all hold to the radical sedevacantist position that there is no pope, and that if anybody says that there is a pope, or that he is in communion with the Holy Father, then he is in communion with a heretic and a heretic himself. By maintaining such a position, which makes no distinctions, and takes no account of the confusion in the Church due to the breakdown of authority, they not only condemn every other Catholic to hell fire, but effectively separate themselves off from all other Catholics, and make themselves into a church of their own. They are truly schismatic. It is consequently entirely illicit to have any kind of association with them. As a consequence of their loss of the sense of the Church, they abandon all sense of hierarchy and structure in the Church. Any bishop can consecrate any other bishop at any time, without authority between them. These bishops constantly ordain to the priesthood men who have no preparation or training, who belong to no religious community, and who are consequently entirely independent of one another and all Church authority. Throwing all canonical norms out of the window, they effectively become just as protestant as the modernists they pretend to defend the Church against.