On 29 April 1943, wildcat strikes broke out in the Netherlands to protest against the Nazi occupation. They started with a walkout at the Stork factory in Hengelo, and quickly spread across the country.
These strike density maps for 30 April and 1 and 2 May are from a report for the Netherlands Institute for War Documentation (P.J. Bouman 1950, De april-mei-stakingen van 1943).
The strikes also played an interesting role in the history of the Dutch trade union movement: https://dirkmjk.nl/en/441/trade-union-growth
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