(ANSA-AP) - BUDAPEST, Hungary — Hungarian Prime Minister Viktor Orban's dominant right-wing Fidesz party is facing a challenge from opposition parties who are backing a joint candidate in many cities in local elections nationwide.

Fidesz has been easily winning local, national and European Parliament elections since 2010, but a more unified opposition and the release of a video showing one of the party's best-known mayors, former Olympic champion gymnast Zsolt Borkai, participating in an orgy on a yacht have shaken up the last days of the campaign.

More than 8 million people are eligible to vote on Sunday for over 3,000 mayors and 17,200 local council members elected for five-year terms.

Incumbent Budapest Mayor Istvan Tarlos, backed by Fidesz, is dealing with a strong push by Gergely Karacsony, supported by five left-wing, Green and liberal parties.

Campaigns in Hungary for upcoming municipal elections have been tainted by candidates' sex tapes, all eged drug use and other scandals, while the most important contest - for mayor of Budapest - is seen by several pollsters as a statistical dead heat. Sunday's vote around the country is also seen as a chance to test cooperation between opposition groups, which in many races are backing a joint candidate to attempt to break the nearly decade-long domination of Prime Minister Viktor Orban's Fidesz party. Analysts say the scandalous revelations about candidates both from Fidesz and the opposition are provoking the interest of voters long-jaded by the constant glut of corruption scandals.

Hungarians will be choosing over 3,100 mayors and 16,000 councilors nationwide.