Nothing much maybe only the federation is a loose join of states or an alliance not a country and a union is one country.
An association is a union of persons or companies for a common purpose or object. Like an employees association. A federation is a union of various unions. Like Federation of Chambers of Commerce or Federation of various Trade unions (may be bank employees unions, civil aviation employees unions, government employees unions, etc.)
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The purpose of the federation level is to coordinate its affiliated unions, settle disputes between them, and serve as the political representative of the union members.
There is no difference between central and union government
The EU, or European Union calls it self a 'Union'. It is usually considered a supra-national Confederation. The difference between a confederation and federation is that in the former the members have the right to leave at any time. It is 'supra-national' because it exists above the level of the member states.
Egyptian Trade Union Federation was created in 1957.
Austrian Trade Union Federation was created in 1945.
Kuwait Trade Union Federation was created in 1968.
All Pakistan Trade Union Federation was created in 1988.
Union of Myanmar Federation of National Politics was created in 2005.
Christian Trade Union Federation of Germany was created in 1959.
All-African Trade Union Federation was created in 1959.