Job offer only for citizen of Ukraine. Is it legal?

Some employers explicitly state in their job advertisements that they “will employ Ukrainians”. This is not a fully permitted practice, as it may result in discrimination against candidates of other nationalities. Employers in such circumstances may face civil and criminal liability. – Bartosz Wszeborowski and Marcin Szlasa-Rokicki comment for Dziennik Gazeta Prawna.

Article: here.