Yes.
It was union involvement at one of my work places that ensured employment law was upheld and contracts were honoured. The union was crucial in defending workers at times. A number of internal practices were changed as a result of their involvement.
Rather not. A company I worked for routinely flouted employment law and gave staff grief over matters they had no right to.
It was when we involved a Union that they were forced to simply obey the law and honour staff contracts.