Once again, companies are not held to the same reporting requirements of a labor union.
Public companies are held to a similar standard.
But why, particularly when you have closed or agency shop requirements should an organization that they
must pay in order to work not have to reveal what it pays people?
What interest does a union have in
not disclosing that information? There is zero compelling argument for not making that information public,
unless the union has the intent of enriching those that run it at the expense of it's dues paying members which pretty much goes against the whole reason of having a union to begin with.
Let's not forget that Landrum-Griffin came about because of the rampant abuse and fraud in the Teamsters, the Longshormen and the Mine Workers in the postwar 40s and 50s. Frankly, this type of behavior (which nicely mimics the behavior of corporate raiders) is exactly
why unions are treated, to a certain extent, like public companies--so they don't screw their proverbial shareholders.
Edited to add:
I get why union officials (or someone in 700's shoes) does not like unionfacts.com--it's clearly anti-union. OTOH, a spot check indicates that their data matches the data from the feds. However, they do things like point out that there are 313 people at the CWA earning more than 75k/year. That's a rather damning statistic and would otherwise be harder to find by simply combing thru the LM-1/2/3 data.