At the Diet of March 1467, two traditional taxes were renamed; the chamber's profit was thereafter collected as tax of the royal treasury and the thirtieth as the Crown's customs. Because of this change, all previous tax exemptions became void, increasing state revenues. Matthias set about centralizing the administration of royal revenues. He entrusted the administration of the Crown's customs to John Ernuszt, a converted Jewish merchant. Within two years, Ernuszt was responsible for the collection of all ordinary and extraordinary taxes, and the management of the salt mines.

Matthias's tax reform caused a revolt in Transylvania. The representatives of the "Three Nations" of the province—the noblemen, the Saxons and the Székelys—formed an alliance against the King in Kolozsmonostor (now Mănăștur district in Cluj-Napoca, Romania) on 18 August, stating that they were willing to fight for the freedom of Hungary. Matthias assembled his troops immediately and hastened to the province. The rebels surrendered without resistance but Matthias severely punished their leaders, many of whom were impaled, beheaded, or mercilessly tortured upon his orders. Suspecting that Stephen the Great had supported the rebellion, Matthias invaded Moldavia. However, Stephen's forces routed Matthias's at the Battle of Baia on 15 December 1467. Matthias suffered severe injuries, forcing him to return to Hungary.