The Owner Of The Restaurant I Work In Threatened To Fire Anybody Who Complains To Corporate

i work at a chain restaurant in the states, just started the job a month ago. heard from the other employees how terrible to owner is but i generally just dont care about that kind of thing, im there to do a job and get a paycheck, thats it. but recently the only night shift lead who happens to be an 18 year old kid has been getting very stressed and decided to complain to corporate over the new manager chewing tobacco while working with food and spitting into the trashcans(the owner knows he does this and has been shown pictures of the spit in the trashcans.)

today my shift lead texted me and said he got yelled at a bunch for filing a complaint and got written up for not cleaning some stuff they never told him to clean, and also said a bunch of other stuff to him about being a liability and a concern, despite the fact that hes the only night shift lead and if he were to quit the store would likely immediately fall apart until they could find a new one, and they refuse to pay for people servsafe certifications so nobody wants to bother for the very miniscule pay increase.

all this to say, the owner stated that shed fire any person that complained to corporate again, as far as im aware this would be considered retaliation, but im also just not that versed in stuff like this and would love some advice, if we file a complaint about something else regarding safety codes and such or about our manager who continues to do these gross things, and they fire us, what can we do?