According to the Polish law, foreigners of any nationality who come to Poland in order to perform research work in PUBLIC research institutions (higher education institutions, research institutes and units of Polish Academy of Sciences) do NOT need a work permit.

However,  non-EEA citizens who come to Poland to conduct research in NON-PUBLIC institutions, are obligated to have a work permit. Work permits are issued by a relevant office (voivod office) in Poland on request of a researcher's future employer in Poland. After receiving the work permit, the employer sends it to the researcher who then needs to submit it along with other documments while applying for the visa for employment purposes to Poland.

Having received the visa for employment and the work permit, a researcher can enter and work in Poland legally.