Quoting Steve Cushion in On Strike Against the Nazis, pages 52–54:
The mass arrests of June 1941, Operation Sonnenwende, do not seem to have greatly intimidated the Belgian miners and metalworkers. Five thousand miners in the Borinage held a two day strike on 17–18 July and 1,500 miners in the Charleroi region struck on 5 August. The Liège region was back in militant action in October with strikes of both miners and the Cockerill steel workers who had played so prominent a rôle in the May 1941 events.
Strikes in various industries, mainly in the French-speaking south of Belgium, continued throughout the autumn and winter of 1941–42. The main grievances were over food and coal rations and heating in workplaces. Le Drapeau Rouge reported around half dozen important strikes every month.¹⁰¹
One area with a particularly militant record was Verviers in Liège province, with strikes in April 1942 starting in the textile industry, then spreading to engineering workers and the railway. There was inevitably widespread industrial action on May Day.
One group of workers who were noted for their early strike action were the postal workers in Brussels. Action in September 1941 resulted in a 10% wage increase and a bonus of 150 francs for the married men. Another strike over Christmas and New Year was also settled to the workers' satisfaction. August 1942 saw another postal strike, this time winning a shoe allowance and a loan of 1000 francs.¹⁰²
July 1942 was particularly active. The strike started in the Basse-Sambre mining basin with 35 pits striking for 10 days losing 200,000 tons of coal production. The action spread to 8 pits in the Charleroi coalfield and several engineering factories in the Centre province.
The Fédération des Métallurgistes de Liège (FML, Metalworkers Federation of Liège), the engineering workers federation of the pre-war CGTB, had fallen into decline and was nearly wiped out by a series of arrests on 23 March 1942.
With the old leaders arrested, a young militant, André Renard, took the lead. He already had a good local reputation from his militancy in the 1936 strikes and he managed to rebuild the FML from the base, encouraging the formation of works committees and distributing a regular stencil duplicated bulletin, Le Métallurgiste. Deportations for forced labour in [the Third Reich] gave the FML its first real test.¹⁰³
In March 1942, the occupying authorities started to recruit forced labour to work in factories in [the Third Reich] as the losses on the Eastern Front led to a labour shortage when German workers were drafted into the Wehrmacht.
Working class opposition to these deportations came to a head in November 1942, starting in Cockerill near Liège again, with a strike against the deportation of workers from the factory. This spread to other local factories and mines and the Verviers rail workers joined the action. The occupation forces took hostages from among the workers, but when this had no effect on the strike, they released them and put back the deportations to February 1943.
The experience of joint action between the Fédération des Métallurgistes de Liège and the Comités de Lutte Syndicale des métallurgistes (CLS) in Liège led first to the CLS being given delegates on the action committee of the FML and eventually to a joint organisation. This fusion gave an impetus to the clandestine workers' organisation in the region and workplace committees were formed in many new factories. By the end of 1943, the FML had 12,000 dues paying members.¹⁰⁴
Strikes against forced labour in [the Third Reich] spread to other regions. At the Fabelta factory in Brussels, [Axis] recruiters demanded thirty women to work in an aircraft factory in Leipzig. All the women went on strike enabling the women who had been designated to flee.
There were reports of a number of other strikes against forced labour in [the Third Reich] in December and January 1943, including tramway and railway workers refusing to transport the deportees. In February, at the ACE factory in Charleroi, 4,500 workers went on strike against the threat to deport 1,200 of them. Also in February there are reports of 60,000 metalworkers on strike in Liège province, the third strike in 3 months.¹⁰⁵
May Day 1943 was again widely celebrated, but this was the last of the large-scale, almost general, strikes. Thereafter sporadic action continued over the summer of 1943 in the mines and engineering, mainly short stoppages, go-slows and delegations to management, normally over wage demands, frequently successful. While the action was mainly concentrated in the more industrial French speaking south, there was a level of militancy in the ports and dockyards of Antwerp and Bruges/Zeebrugge.
The final widespread action started in October 1943 with a campaign for a 2000 franc bonus. This seems to have struck a chord with many workers and Le Drapeau Rouge has a significant list of workplaces involved, including the inevitable Cockerill, but also in workforces not previously much involved, including the Flanders textile industry and the railways. This campaign had mixed results but with some reported successes.
In 1944, the massive aerial bombardments by the Allied air-forces disrupted production more or less completely and forced the workers' organisations onto the defensive, mainly pushing demands for pay for time spent in air-raid shelters. During this period, the PCB seemed to lose touch, concentrating on calls for the formation of Milices patriotiques and for L'Insurrection nationale, calls which did not elicit a great response. Those workers who were likely to take up arms seem to have done so already.
(Emphasis added.)