May 1st in Indonesia is, unlike in most of the World, not an official holiday. This obstacle was turned into a opportunity for a show of strength by the Indonesian worker movement, by carrying a part-journey general strike in order to march through the main cities of the country.
Some half million workers marched in red colors, several times the numbers mobilized in 2012. There is context of growing strikes, including a million people general strike last October, that explains this mass participation.
The mobilizations began in 2011 when 9 miners were shot down within a three month strike in the colonial possession of West Papua, in 2012 the class conflict also flourished in Java, with strikes and road blockades, as well as vigilante pickets that applied popular justice to the most abusive capitalists. Further mobilizations impeded the hike of fuel prices decreed by the government.
Source and more details: In Defense of Marxism.