That sounds a bit like (apologies for the strawman): "small business needs to be able to exploit employees to survive."
If small business can't survive without that, perhaps the problem lies elsewhere?
For employees, working at a large company that has already achieved economies of scale is probably a better paycheck -- they have the budget to be able to pay you better.
For society, though, we definitely don't want those small businesses (which don't have the same efficiencies or economies of scale) to be boxed out by large corporations across the board.
Not that this means that we shouldn't have pay transparency (people can and should be able to make their own decisions), but the inability of small businesses to match the salaries of huge corporations is pretty unavoidable.
Transparent pay is great for the employees, but it's still a downside to the company.
Not
I don't follow - to rephrase what you're saying, it's bad for small business owners because their (underpaid) employees will be paid more by (larger) other businesses?
Sounds like the employees of said businesses will overwhelming benefit if what you're saying is true.
And it would make poaching of employees from small businesses easier because they suddenly know about the salaries that they didn't have a clue about before? I don't know what you think the recruiters at of the big players do all day, I would bet they have very good ideas what all the other players pay. If anything it would help small businesses who don't have the money to pay top recruiters.
Also, it's bad for small business owners, because then the large businesses could see what they are paying and much more easily poach employees.
Edit: To clarify, I'm absolutely in favor of pay transparency laws. But any time you make a government policy, there are always winners and losers. It's always a balance between how much you're harming the losers and who they are. In this case, the losers would be the businesses and their owners, which is all that I'm pointing out. But I'd say that the employees should be the winners here, and I say this as a business owner myself.