1938 New York City truckers strike
The New York City truckers' strike started on September 15, 1938, as an unsanctioned strike by some of NYC's Teamsters members, with union leadership initially opposing it. It was caused by a contract expiration, demanding lower hours at the same weekly pay and by its end somewhere between 30,000 and 35,000 strikers were directly involved.
Source: Wikipedia — 1938 New York City truckers strike (CC BY-SA 4.0)