Hosius conceived of the idea of bringing in the Jesuits. At his request the first group arrived in 1564 and was settled and endowed in Braunsberg. Slowly the Order was spread to all Poland, endowed with churches, hospitals and schools. Its goal was to restore Papal supremacy regardless of Polish national interests, individual human rights, and moral principles. He, with other Jesuits, argued that the Warsaw Statutes of 1573, were a "criminal conspiracy against God" and should be abolished by the King. He openly recommended to King Henri de Valois to retract his oath maintaining that an oath given to "heretics" may be broken even without an absolution. He even commissioned the King's confessor, William Ruzeus to explain to the King his "duty" to break the oath. Papal Nuncio Gratiani, advised the King to crush religious and political liberties, offer offices only to Catholics and to engage in a war with Muscovy to keep the nation from religious discussions and intellectual pursuits.
Sounds like he did his job well. Still doesn't prove he wrote this alleged letter.