Ks. Michal spent at least part of his career in the United States. Records show his having been an assistant at St. Stanislaus B.M. Parish in Buffalo, NY in 1895 and administrator of St. Casimir Parish (also in Buffalo) in 1897. By 1900, Slupek was serving in the Archdiocese of New York as the first resident pastor of the newly formed St. Casimir Parish in Yonkers. While there, he was instrumental in the purchase of four acres of land for the parish complex and had the church society incorporated. In the latter part of 1901, Slupek was assigned to serve as the first resident pastor of Staten Island’s St. Adalbert Parish. During his tenure there, he was responsible for purchasing land for the parish church and beginning the building’s construction.

Slupek’s next assignment was to St. Joseph Parish in Florida, NY. This rural community, once a marshland, became a thriving onion production center for the East Coast once the Polish immigrants settled there and reclaimed the land for cultivation.

Slupek’s name is also associated with St. Joseph’s Immigrant Home in New York City, a place of refuge for the thousands of Polish newcomers to this country. (The responsibility of running this home was in the hands of the Felician nuns, Buffalo Province.) Besides being a regular contributor, Slupek served as the home’s chaplain.

An article in the Polak w Ameryce, dated September 30, 1903, stated that Ks. Slupek pastor of the Polish parish in Chester, PA (St. Hedwig) had left for what was believed to be a permanent stay in Galicja. The centenial album of Brooklyn’s St. Casimir Parish noted that while in Galicja, he helped recruit seminarians and priests for the Archdiocese of New York. (Two known recruits were Rev. Gerwazy Kubec who became pastor of St. Casimir’s [1912-1953] and Rev. Jozef Rysiakiewicz.)