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Yes they contribute to campaigns
One method used by unions to increase their power and influence is to accumulate money, then use that money to buy political influence.
Unions gained political influence.
labor unions
Unions gained political influence.
Labor Unions have specialized roles and responsibilities in the United States and abroad. At the institution level they serve to offer representation and counsel to workers before the management. In the social and political level Unions use their lobby powers to influence public policy.
Knights of labor
Unions gained political influence
There are limits on the amount of money they can give to a candidate.
They all influence thousands or millions of people.
Try http://www.photius.com/countries/south_africa/government/south_africa_government_trade_unions.html
Trade unions influence a business by trying to get businesses to buy certain products. Trade unions also try to influence the amount a person is paid.