There's definitley nothing wrong with changing or lowering commission percentage, but the thing is, first of all at the start of their affiliate program they should point out that the commission rate is not fixed and can/will be changed, and even after that every participant should be notified about every single change in this rate by whatever medium they use for communicating with their users.
I really don't know what happened to this case but as I read their terms and conditions they stated in Miscellaneous and other significant terms that "FortuneJack reserves the right to amend, cancel, reclaim, or refuse any promotion at our discretion." so technically they can change the rules whenever they want.
They must abide the rules to their affiliates before creating a new one.
Since it is stated in their terms and conditions then they have the right to amend or cancel any promotion offered on their site. It it there before the player and user who registers an account with them has to confirm they understand these terms before they are allowed to complete registration.
So I dont see anything coming out of it if they decide to fight them for their affiliation payments.
Even if your terms and conditions say one thing, it still doesn't mean that you can retroactively change them. If you were supposed to be paid one thing, and then months later (when your due to get your affiliate payment) the terms are changed and you're told your being paid less, then that's a scam.
The correct thing to do, would be to say we're paying x terms until month end and then phasing in this new program. If you'd like to stay then stay, and if not alright. That would still leave a bad taste in the mouth of affiliate programs, though it would be fair enough to them to not waste their time if it's not financially worth it anymore.
As a complete side note: most terms and conditions don't hold up in court, as they typically violate local law. Hopefully DT comes here and checks this all out.
EDIT:
Quoting below what is alleged occured from FortuneJack.
In January 2019, FortuneJack forced unfair, retroactive terms and conditions onto their affiliate marketing partners in a very sneaky way. They tried to paint it in a positive light, with a subject line that read, "Become a Member of Club40!" Sounds cool, right?
Wrong. The devil is in the details, and after taking a close look at the fine print, it's clear that "Club40" is nothing but a big, greasy turd.
Under the original terms and conditions, an affiliate of FortuneJack would earn at least 25% from their referred players. This was a fair deal -- pretty standard in the industry for a starting rate.
With Club40 -- which seemed like a choice, but was actually the name of their mandatory new commission structure -- most affiliates will earn only 10% on their referred players.
But it gets worse. This extremely low rate isn't just for any new players sent after Club40 went into effect. It applies to all players ever sent, including those referred under the previous T&Cs where the affiliate was supposed to earn at least 25% for the life of the player.
This is a classic bait and switch, and certainly not the way an ethical, professional company should behave. This is why we have rogued them here, and this is why FortuneJack is rogue at Affiliate Guard Dog as well.
In addition to the above, FortuneJack is refusing to pay commissions to their affiliates. You can read about them refusing to pay at least one affiliate in the thread above (in post #3).
Making one-sided retroactive changes to a contract is never acceptable, and refusing to pay what they owe is a big red flag.
Avoid FortuneJack at all costs.