UPDATE!National Bank of Ukraine according to the  resolution  № 381 dated 25.09.2013

obliged to transfer the entire amount of currency earnings of exporters to the hryvnia:       

    "Require mandatory sale of  earnings receiving from abroad  by legal entities (which are not banks) and individual entrepreneurs on the interbank currency market of Ukraine "

       This document came into force after publishing – on the 12^th of October  2013