In February 1919 the Catalan Regional Conference (part of the CNT, an anarcho-syndicalist union) organized a strike at the Barcelona offices of a Barcelona electrical company, because they fired people for attempting to form a union.
When they didn't listen the CNT escalated and organized a strike at the electricity generation plant. This plunged Barcelona into darkness and stranded trams on the streets.
So the Spanish state send in the military to restore power.
So naturally this caused the strike to further escalate now including most of the city's gas, water, and electricity workers.
Not to mention the solidarity strikes, outside of Barcelona, happening in Sabadell, Vilafranca and Badalona.
On March 8 the Spanish state responded by militarizing the reservists working in these fields, threatening them with being confined to barracks, if they don't break the strike.
Which of cause ended in the only obvious consequence.
The tram workers and carters who transported essential goods also joined the strike.
And almost none of the militarized workers broke the strike leading to the government locking 800 of them up.
These workers were than supporterd by the printers union, which refused to publish the proclamations of the Spanish state or articles that opposed the strike.
Not even the statement by the company saying that everyone who wouldn't return the work would be fired was printed.
Throughout this whole strike the CNT sought to win their demands by mobalising a lot of large amounts of workers and using tactics like sabotaging the transformers and power cables.
At this point the CNT's strike committee were in a position where they could negotiate with the ruling class and force them to increase wages, pay worker's wages for the period that they had been on strike, recognise the union, grant an eight hour day and reinstate fired workers.
This whole thing was so threatening that the prime minister declared the 8 hour day for the whole construction industry (and later expanded it to all industrie) just to calm them down.
This is a great example of how solidarity can be an extremely strong weapon, being able to shut down whole city's.
A following strike to release a number of prisoners who were not released sadly failed, through state repression using martial law, but what was achieved is still incredible. And it is also absurd how much the strike grew. Remember this conflict started with a company firing a couple of people for trying to build a union.
(Source: Means ans Ends: The revolutionary Practice of Anarchism in Europe and the United States. by Zoe Baker)