What is FSSP?

What is FSSP? And why are they prohibited from celebrating in some Diocese (at least, that’s what I heard)?

Here is the link to he international headquarters:


and to the North American headquarters:


and the general info


 **In 1988, Pope John Paul II canonically established the Priestly     Fraternity of St. Peter as a society of apostolic life and approved its constitutions. The     Fraternity was founded in response to the Holy Father's call to ecclesial unity and the     new evangelization. Hence, our name denotes a filial love and loyalty to the Supreme     Pontiff.**

Kewl, most thanks!

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