There should of course be no laws requring an employer to prefer non-union workers over union members in hiring or promotion. A decision to support "labor" or not should be between the employer and employee, like any other labor contract, and the government should have nothing to do with it except to protect the justly acquired property of everyone concerned.
That being said, demands to repeal "right-to-work" are woefully incomplete. If employers ought to have a right recognised to hire union members exclusively, then they also should have their right NOT to hire union members or not to recognise or "collectively bargain" with unions as well.
It cuts both ways!
Workers also have every right to join, or NOT to join, a union of their choice. In their quest for employment, they have every right to offer inducements (such as longer hours or lower wages) which I think come under a "right-to-work" as much as any union benefits that may be offered. These rights have been badly abrogated by pro-union legislation like the Davis-Bacon Act, the Norris-Laguardia Act, the Wagner Act, etc and "minimum wage" legislation.
Those critics of right-to-work would make a much better case for themselves if they would demand repeal of the above legislation, most of which played a part in making right-to-work seem necessary as a counterweight to union power after WWII.
How about it, Comrades? Are you willing to demand freedom for workers all the way around, or just where employment of your own is concerned?
PEACE AND FREEDOM!!
"The worst thing that can happen to a good cause is not to be attacked successfully, it is to be defended badly". F. Bastiat
"First they ignore you, then they laugh at you, finally they attack you, and then you win"! Mohandas Gandhi