New Landlord Is Adding A Pet Rent In The Middle Of Lease

Location: Washington State/US

My apartment building recently went from being owned by a local man to a large California based management company. This is the third time they have tried to create new rules that are in violation of my current lease and/or state law.

1. Trying to claim that any rent not paid on the first of the month will incur a late fee. (In Washington State you have until the 6th before any late fees can be applied.)
2. Creating a new parking pass system. Nowhere in my lease does it mention parking passes, I just have to have my vehicle registered with the office.
3. And finally we get to today's notice - the new $50 dollar "pet rent effective August 1st, 2026." I know for a fact that this isn't legal. It equates to a rent increase outside of the lease agreement. Nowhere in my lease is a pet rent even mentioned, only an extra pet deposit.

My wife has gone over to talk to them about the parking pass, and they revealed that they have almost zero prior documentation surrounding the tenants in my building. So no pet declarations, no vehicle registrations, and seemingly no leases.

My question is how illegal is this? Would most lawyers take the case if my neighbors and I pursued it? Or would the management company be able to just say "sorry our bad we'll stop, but we're gonna do it when your lease runs out anyways," and get away with it?

edit: they also tried to require renters insurance for all tenants. Which isn't a bad thing to have, but it's not in my lease. So I'm not liable for them having bad insurance.

Also to clarify: these notices were posted on every door in my complex and presented as 'effective as of the following month' NOT on a case by case/new lease signing basis.