De Las Casas was pretty scathing about the numerous abuses of Spanish colonialism, but none received more of his ire than the notorious encomienda system. What was supposed to be an arrangement that benefited both colonialists and indigenous people alike turned out to be little better than slavery. Native laborers were treated appallingly.

Under the encomienda system each Spanish colonialist or encomendero would be granted a certain number of indigenous laborers, who would pay tribute to him in exchange for protection. However, as De Las Casas soon discovered, the system was little better than slavery. Indigenous workers had no choice in their "employment"; they were forced to perform hard labor for their colonial masters, often under the most appalling conditions.

In his numerous letters De Las Casas named individuals and institutions and accused them of exploiting indigenous people; to him, their behavior was positively sinful. The encomienda system epitomized the sins that the Spanish people were committing in their colonial endeavors. De Las Casas believed the horrible system would one day come back to haunt them with devastating effect. De Las Casas hated the encomienda system so much that upon his arrival in the Americas he forbade absolution to be given to those who held indigenous people in encomienda.