In 2012, the Simon Wiesenthal Centre included both Tyahnybok and Myroshnychenko into its 2012 Top Ten Anti-Israel/Anti-Semitic Slurs: Mainstream Anti-Semitism Threatens World Peace.
That's what the SWC wrote on Tyahnybok:
In recent elections the radical right party won 41 [AS: in fact: 37] seats in the Ukrainian Parliament (10.44% % of the popular vote). Tyagnibok has called for purges of the approximately 400,000 Jews and other minorities living in Ukraine and has demanded that Ukraine be liberated from what he calls, the “Muscovite Jewish Mafia.”
As far as I know, Tyahnybok has never "called for purges of the approximately 400,000 Jews and other minorities living in Ukraine". Yet he had indeed referred to the "Muscovite-Jewish mafia" in 2004, i.e. eight years before his party entered the parliament for the first time.
And then on Myroshnychenko:
MP Igor Miroshnichenko, recently labeled noted Ukrainian-born American actress Mila Kunis, a ‘zhydovka’, (dirty Jewess). Zhid is an insidious slur used against Jews since the times of the Czar and invoked by the Nazis and their collaborators as they rounded up the Jews to murder them at Babi Yar and in the death camps.Myroshnychenko has indeed called Kunis a "zhydivka", but not "dirty zhydivka". While this term may be considered an abusive or rude word in modern Ukraine, it is irresponsible and, eventually, disingenuous to link the use of this word to "the times of the Czar" or the Nazis or the murders of Jews during the WW2.
Thus, in the end, we have two instances of using rude words ("zhydivka", "zhydivs'ky", etc.) which are abusive to Jews, but does this constitute a case for banning two Members of the Ukrainian Parliament from entering the US where the Constitution protects not only abusive words but also hate speech? I doubt it.
Furthermore, while the Svoboda party does include members who hold anti-Semitic prejudices, the party itself, i.e. as a political organisation, is not anti-Semitic. It is ultranationalist and is clearly on the far right of the Ukrainian political spectrum, but it does not propagate anti-Semitic policies in its political programme.
If the rumours about banning Tyahnybok and Myroshnychenko from entering the US on the basis of two cases of them using rude words are true, then it is an unfortunate development and I would urge the Ukrainian government to inquire into the grounds of discrimination against the two legitimately elected Members of the Ukrainian Parliament.
UPDATE:According to Radio Svoboda [in Ukrainian], the US Embassy does not have any order to bar Tyahnybok and Myroshnychenko from entering the US. Most likely, the rumours have been started by the Party of Regions to put Svoboda at loggerheads with other parties in the United Opposition.