His rule was marked by bitter conflicts, especially against his brother, Duke Abel of Schleswig who seems to have wanted an independent position and who was supported by the counts of
Holstein. Eric also fought the
Scanian peasants, who rebelled because of his hard taxes on ploughs, among other things. The number of ploughs a man owned was used as a measure of his wealth. This gave the king the epithet "plough-penny" (
Danish:
Plovpenning). Eric had only been king for about a year when he first came into conflict with his brother, Duke Abel of Schleswig, in 1242. The conflict lasted for three years before the brothers agreed on a truce in 1244 and made plans for a joint
crusade to
Estonia. At the same time Eric faced trouble from the religious orders who insisted that they were immune from taxes that Eric might assess. Eric wanted the church lands taxed as any other land holder would be. The Pope sent a
nuncio to negotiate between the king and the
bishops at
Odense in 1245.
Excommunication was threatened for anyone, great or small who trespassed upon the ancient rights and privileges of the church. It was a clear warning to Eric that the church would not tolerate his continued insistence at assessing church property for tax purposes. King Eric retaliated immediately, reconquering the city of
Ribe and occupying Abel's patrimonial city of
Svendborg the same year. In 1247, he captured
Arreskov Castle (
Arreskov Slot) on
Funen, as well as taking Christopher and Canute prisoners. A truce was arranged by Eric's sister Sophie of Denmark (ca 1217–1247) who was the wife of
Johann I, Margrave of Brandenburg (c. 1213–1266). The terms of the accord left Eric in firm control of all of Denmark. In 1249 the peasants in
Scania rose in rebellion against the plough tax. The king restored order with help from
Zealand, but the church, Duke Abel, and the German counts in southern Jutland were pushed into an erstwhile alliance against the king.{{cite web|url = https://danskefilm.dk/lokation.php?id=247 ==Regicide==