The move comes after three years of complex negotiations between the Vatican and the Society of St Pius X and was revealed just as Pope Benedict XVI appointed a high-profile American archbishop to a key post to oversee relations with traditionalists.
A letter by Fr Christian Thouvenot, secretary general of the SSPX, to SSPX bishops and regional leaders was leaked on the Internet on Tuesday. Thouvenot later confirmed its authenticity.
The letter says the SSPX superior general, Bishop Bernard Fellay, told the head of the Vatican doctrinal office, American Cardinal William Levada, that "he couldn't sign" the Vatican's doctrinal offer during a meeting on June 13.
Benedict has actively sought reconciliation with the group since his election to the papacy in 2005. In 2009, he lifted the excommunication of the four SSPX bishops and started doctrinal talks in the hope of healing a decades-old rift within the Catholic church.
The negotiations led to a Vatican proposal that was delivered to Fellay in September. The "Doctrinal Preamble" was aimed at overcoming the doctrinal differences between the Vatican and the group, which rejects the modernizing reforms of the Second Vatican Council (1962-1965), including church acceptance of ecumenism and religious freedom, and its rejection of anti-Semitism.
In his letter, Thouvenot writes that Fellay proposed his own version of the Preamble last April which, "according to several agreeing sources," seemed to "satisfy the Supreme Pontiff."
But he added that cardinals in Levada's Congregation for the Doctrine of the Faith "amended" the text and it "now reintroduces, substantially, the propositions of September 2011."
During his June 13 meeting with Levada, Fellay "immediately informed him that he could not sign this new document," which he deemed "clearly unacceptable."
The SSPX will hold its general assembly in early July to discuss the issue.