Discrimination against Irish immigrants targeted their Catholicism, relative poverty and willingness to work for lower wages than the average native American employee. Nativists accused the Irish of having greater allegiance to the Church in Rome than to the United States. They were also incensed by what they perceived to be the influx of cheap labor displacing them in the workforce.
The biggest factor in the anti-Irish sentiment of the 19th century was the Catholic faith of the immigrants, according to the U.S. Embassy. Catholicism had a long history of antagonism with Protestantism and Anglicanism in Europe that carried over to America in the 1820s. Not only did the typically Protestant nativists deplore the doctrinal peculiarities of Catholicism; they believed it to be incompatible with American democracy. Nativists argued that a hierarchical, centrally-governed church went against the pluralism that made the American republic workable.
Discrimination against Irish immigrants had strong economic motivation as well. The Irish fled conditions of immense poverty in their native land. Upon arriving in the United States, they were willing to work for less money than employers paid the typical laborer. Nativists resented the threat to their livelihood, according to the Library of Congress.
Additionally, nativists believed that the poor Irish immigrants would not rise above poverty. They feared the Irish would become America's first permanent working class. This seemed to threaten the pivotal American principle of social mobility.