Who may file a complaint?

The Law on the Election of the President (asof 2013, in Ukrainian)

Source: http://zakon2.rada.gov.ua/laws/show/474-14

Article91 A candidate for the President of Ukraine, a party (electoral block)which is a subject of the electoral process, election commission, a voter whose voting rights or interestswere violated by a decision action or inaction of the subject of the complaintcan be a subject of the appeal. A proxy can also file a complaint on behalf of the candidate forthe president.