There are already companies collecting such information and making them available for their customers (who supposedly provide some collated data set to them in exchange). That's what all the "paying top of market rate" talk in various companies is based on.
So: the potential for collusion already exists, but unless regular folks can get access to the analysts' data sets as well, it's a very one-sided deal.
You don’t even always need a third party. My wife works in HR for the government and part of her job is literally to contact neighboring counties and send them requests for their salaries for various positions and levels while filling out salary requests from other counties.
Of course, being government, it’s all public information anyway so collaborating in this way is seen more of a performance increase vs manually accessing each counties salary information but it’s the same premise.
So right now all the companies do share salary data with each other. They typically wash it through a 3rd party so it's not that blatant.
So, a change where the companies also posted their salary data publicly would only additionally inform employees not HR. But yes tech-HR has in the past gotten in trouble over salary fixing.
Exactly the contrary: if all wages are public, that wouldn't be possible, because only one company would have to violate that conspiracy to get all employees at other companies to start applying to them.
No, because they need to attract employees and employees would generally not be attracted to uncompetitively low compensation packages.
As a result, companies absolutely track how much employees of a type and level get paid elsewhere, so that they know where to aim compensation packages competitively.
Not sure if the parent's concern is valid but I think the argument would be that companies can conspire to all suppress wages so they don't have to compete on comp. That would be hard to do now because they can't "officially" conspire in this way (eg sign a binding contract with each other) because that would be illegal. Without an enforcement mechanism it is too easy for any one company to defect from the "gentleman's agreement" and offer higher wages. If all salary information was public though, then as soon as one company defected and offered one high-value employee a higher salary everyone else would immediately know it and start competing on salary again. So that makes the informal agreement more stable and leads to lower wages.
So: the potential for collusion already exists, but unless regular folks can get access to the analysts' data sets as well, it's a very one-sided deal.