Usually when hired, if the boss is an effective supervisor, you will be told what is expected of you either directly by boss or your designated trainer. OP, if you feel overloaded doing what you were told was your job responsibility then the job is a bad fit and the blame is on you and your supervisor - You for taking job you cannot perform and boss for hiring someone who cannot perform the job… On the other hand, sometimes an ineffective supervisor faced with not being able to hire all the help they need starts overloading their employees with additional work - Which can reduce the quality of the work done and burn out the employees. Both of these things will ultimately impact the business. OP if the problem was you misunderstood the job expectations and were unable to perform them, then while regrettable; what the supervisor did is not unexpected. On the other hand, if boss is just layering on more and more work than the job you were hired to do because they think they can get away with it; or for business reasons, they are not able to pay for more help then you have good reason to complain. And if that was the case you would have been wise to have been looking for another job… Ultimately in a free enterprise system, economics makes the important calls. A business owner or manager who drives away workers or fires good workers will not survive in the long term. Unfortunately that reckoning comes not as fast as you would like.

That sounds like constructive dismissal. Contact an employment lawyer.