Since you needed an immediate answer, this may well be too late to help out, but a quick first try might be usa.gov. The search "Tompkins Square Park" and labor and history gets 2 hits. The first one, "Landmarks Preservation Commission June 20, 2006, Designation List 377..."
(www.nyc.gov/html/lpc/downloads/pdf/reports/ps64.pdf)
says on page 12: "As early as 1874, a “rally of unemployed workers was broken up with some violence by the police.”74 This early “Tompkins Square Massacre” presaged the more recent confrontation that took place in August 1988 and became known as “The Battle of Tompkins Square"

The reference number 74 is Malve Von Hassell, Homesteading in New York City, 1978-1993. The Divided Heart of Loisaida (Westport, CT: Bergin & Garvey, 1996), pp.43-44

You may be safer going with the broader search: "Tompkins Square Park" history (10 hits), or even "Tompkins Square Park" (44 hits), to be sure you don't miss something relevant that uses slightly different words. My rule is "the more words you use, the bigger chance one of them will be the wrong one", so I try to use just 2 or 3 words that pin down what I am looking for, without producing thousands of hits.

Jim Miller
jmiller2@umd.edu