Unions have grown too strong over the years, and a corrupt union is just as bad as a corrupt business.
Unfortunately unions have never done anything positive for me, and have done several negative things (for instance, in one position I worked you HAVE to pay union dues as an employee whether you are a member of the union or not - as far as I'm concerned that's stealing). When I was doing white collar work I had days of sitting around waiting for a union drew to move materials from the dock to my work space. The dock was 30 feet away, but I wasn't allowed to touch the stuff since the union contract required that only union employees could move materials from one place to another. Same story working in convention spaces and trying to get power, networking, or phone lines put in for a booth - only can be done by the union. Then I've had family members who were fired from their job because they could be replaced by lower paid employees, which is against the union contract, yet the union decided not to enforce the contract.
Then there are the times when the unions and the company work together. In one case the company was going to be behind in delivering on a contract for a customer, which would cost them millions in late penalties. Their solution? Pay the union to strike. The customer contract is written that delays caused by unions don't result in penalties. The workers were NOT paid for the days they struck, and the "result" of the strike was some trivial concession from the employer. Of course the union itself got a huge check as a concession of the strike, but the employees were used as toys and ultimately lost days of pay.
These, and many more issues, have pretty much turned me against unions in general. While I know they've done great good for workers in terrible conditions, they have grown too large, and now exist not to support the workers, but to support themselves.
This signage requirement is utterly stupid, and simply signifies the growth and power of the unions.