MOSCOW — This was supposed to be a moment of triumph for Ukraine. In just over a month, it is to become the first former Soviet republic to host the European soccer championships, an achievement its leaders hoped would showcase its emergence from an authoritarian past and its embrace of Western values.

Instead, it has devolved into one of the most serious diplomatic disputes in Ukraine’s post-Soviet history.

On Wednesday, Austria announced it would join a growing list of European countries and institutions whose leaders are planning to boycott championship matches in Ukraine in protest over the imprisonment of Yulia V. Tymoshenko, a former prime minister who supporters believe has been targeted for reprisals by her main political rival, Ukraine’s president, Viktor F. Yanukovich.

This week, José Manuel Barroso, the European Commission president, said he would also cancel plans to travel to Ukraine, after similar announcements by the European Union’s justice commissioner and a host of less prominent European lawmakers. Germany’s chancellor, Angela Merkel, has said that she is still considering her position and that she will decide closer to the start of the event, called Euro 2012, on June 8.