Well, it is not that simple, the unions in France have substantial power but rather modest membership:

France

Collective Bargaining Coverage: 98%

Proportion of Employees in Unions: 8%

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Sweden

Collective Bargaining Coverage: 88%

Proportion of Employees in Unions: 70%

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United Kingdom

Collective Bargaining Coverage: 29%

Proportion of Employees in Unions: 26%

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From https://www.worker-participation.eu/national-industrial-rela...