Well, let's put it this way: it wasn't there as recently as last year at Frontier (the only place I've been employed in that time span); the same change was made in my wife's healthcare plan at her (non-airline) place of employment; both plans cite the Affordable Care Act as the reason behind it.
Now, I did say "more or less"--companies are free to absorb that if they choose. But it's not spuriously "somehow linked"....