What's the issue if it only applies to contractors?
I'm very pro-union btw but my understanding is that IR35 doesn't apply to FTEs, so no need for full union rights - at least in the case of short-term contractors (who choose money and flexibility over security). Agency temps (on equivalent or lower pay than FTEs) are a different matter and may need protection. Long term contractors are disguised FTEs so their choice again, probably not normally an issue.
But perhaps I'm misunderstanding the law or the point?
The IR35 has been changed so that now client / deemed employer can decides if employment rights can be afforded.
Whether to hire someone as an employee, on FTE or in-scope IR35 is a business decision. If businesses wanted everyone could be hired as a "contractor" without employment rights from tomorrow. It's not like workers have a choice now, apart from looking for a job elsewhere.
I'm very pro-union btw but my understanding is that IR35 doesn't apply to FTEs, so no need for full union rights - at least in the case of short-term contractors (who choose money and flexibility over security). Agency temps (on equivalent or lower pay than FTEs) are a different matter and may need protection. Long term contractors are disguised FTEs so their choice again, probably not normally an issue.
But perhaps I'm misunderstanding the law or the point?