"voluntary union" is a correct and usable phrase in written English.
You can use it to denote a union of two parties that are willingly joined together. For example, "The voluntary union between the two churches strengthened their shared community."
The euro crisis was mishandled and lasted a long time, and it turned a voluntary union of equals into something quite different".
In general, modern marriage is best-described as a voluntary union, usually between a man and a woman (although there are still vestiges of the arranged marriage that once flourished in eastern Europe and Asia).
Conceived as a voluntary union of peasants, the kolkhoz became the dominant form of agricultural enterprise as the result of a state program of expropriation of private holdings embarked on in 1929.
Though such a liberal view of divorce was unacceptable in Milton's era, it struck a more responsive chord in those countries where at the turn of the 21st century marriage was understood as a voluntary union between equals.
If the idea of Britain is anything, it is that it is a voluntary union and it's no bad thing for that choice to be remade by a new generation.
The governance of England, Scotland, Wales and Northern Ireland should be reinvented within a new voluntary union in a bid to save the UK from disintegration, an independent all-party group of experts will argue this week.
Addressing the problem of employers' noncompliance with arbitration decisions, Reeves devised a system in which participation was voluntary for unions but compulsory for employers.
"But when I tried to change things as an assistant superintendent, it didn't have much impact because it was voluntary and the union didn't like it.
In this respect, Scotland is very different from Wales, which was forcibly incorporated into England over 400 years before the Scots signed a voluntary Act of Union in 1707.
The commission, set up by the centre-left thinktank Compass, with funding from the Joseph Rowntree Charitable Trust, will bring together leading figures from business, voluntary organisations, trade unions and academia.
Future of Labour: Party must rediscover radicalism and become a movement and a cause, give members a proper voice, reach out more to trade unions, voluntary sector, community and environmental groups, move beyond old Blairite/Brownite divisions to unite around ideas, believes a third of shadow cabinet should be women but would also support Harriet Harman's 50% proposal.
