Being a vegan in Poland can be hard because there is a lot of people who do not tolerate that some are different from others. However, it is not impossible, and there is a strong tendency for the number of vegans in Poland to grow. You will still encounter many folks (especially in small localities) who barely know the concept of, or the term veganism, as well as vegetarianism.
Nonetheless, there are quite a few vegan or vegetarian restaurants, espeially in bigger cities.
The best known Polish group promoting veganism is EMPATIA.
There are also some other groups promoting veganism and vegetarianism in general, including an amateur sports team, Vege runners.