It depends on what you mean by "unfair".

In plenty of companies I have worked for, you pay quite a lot more than you want for a particular hire not necessarily because they are worth it but because you are desperate and they are nearly good enough. You generally don't get away with putting people's salaries down if they don't perform and if you did, they might leave ending with you being back in the mess.

This might be magnified in smaller companies but it could easily squew salary figures and depending on their sex, it could also make the figures look really wrong.

This might be "unfair" by one definition but it definitely happens and is one reason why it is hard to be transparent about wages. It can also create resentment if others knew that someone was overpaid.

Word about salaries gets around via the employee rumor mill. The new highly paid employee will tell their co-workers over drinks, or accidentally leave a pay stub on their desk, or someone in HR gossips with their friends. Trying to keep secrets never works when there are no real penalties to prevent it.

In the US at least, employees are explicitly allowed by federal labor law to discuss compensation with each other. Employers generally can't retaliate against them for doing so (although like all labor laws that one is occasionally broken).

'It depends on what you mean by "unfair".'

Can it be explained on the basis of value? If so, then good. If not, then it's likely unfair.

"It can also create resentment if others knew that someone was overpaid."

How can they be overpaid? The salary was set by the market. If the others are underpaid due to lagging the market, then they might just leave anyways. Their value has changed during their tenure and the company has not adequately adjusted for that to stay competitive in the market.

bingo, I've gone from about $56k to $130k in about 8 years by changing companies. I know another guy who stayed with one of the companies for about 30 years. He was making less then me when I got hired, but about $15k and now he's at about $70k.

This should really end. Job hopping should not be necessary to get a decent wage.

Good job reaching for a maybe "acceptable" edge case. In reality we know it's the drunk sales guy with 3 divorces who needs to pay child support and is buddy-buddy with the CEO skewing the figures.

My experience with union guys is that the contractors know who is good and who isn't, and the bad or slow workers get a lot less work or get returned to the hiring hall in favor of a different worker.