The original manuscript is not extant here but probably read works. Scribe 2 of 𝓟 initially copied the word as work, but then almost immediately afterwards inserted inline the plural s (there is no change in the level of ink flow). As noted under Alma 7:24, scribe 2 frequently miswrote works as work.
Usage elsewhere in the text shows that either work or works can occur with the prepositional phrase “of justice”:
Overall, the text is evenly divided between “the work of justice” and “the works of justice”; in each case, the critical text will follow the earliest reading.
Summary: Accept in Alma 12:32 the plural works, the virtually immediate correction in 𝓟; usage in Alma 42:22 supports the plural usage “the works of justice”.