Allow property owners the right to use their property as they wish and unions will evolve into extinct decomposing crap.
There will never be an ABSOLUTE right for property owners to use their property as they wish, it would result in anarchy, the exact opposite of intent.
Also, we will never be rid of government, so the logical solution is equal protection under the law.
Government favoritism is the union advantage. Without it, unions would have to offer contribution rather than obstruction, to elicit agreements.
Both business and unions seek government favor and protection, and both deserve neither.
Government and government favoritism are the problem, and when the favoritism goes, the market will correct the balance.
Unions will continue, as long as they supply a product of value, a highly skilled, trained, productive worker, (though they will probably call themselves "associations" rather than unions, and skills would not include tenure or seniority).