Tommaso Caccini, a Dominican friar, appears to have made the first dangerous attack on Galileo. Preaching a sermon in Florence at the end of 1614, he denounced Galileo, his associates, and mathematicians in general (a category that included astronomers).
In late 1614 or early 1615, one of Caccini's fellow Dominicans, Niccolò Lorini, acquired a copy of Galileo's letter to Castelli. Lorini and other Dominicans at the Convent of San Marco considered the letter of doubtful orthodoxy, in part because it may have violated the decrees of the Council of Trent: ...to check unbridled spirits, [the Holy Council] decrees that no one relying on his own judgement shall, in matters of faith and morals pertaining to the edification of Christian doctrine, distorting the Scriptures in accordance with his own conceptions, presume to interpret them contrary to that sense which the holy mother Church... has held or holds... — Decree of the Council of Trent (1545–1563). Quoted in Langford, 1992.