In an interview published on 15min.lt news portal on Monday, said the incident had occurred five years ago in a studio after a casting.
"We stayed afterwards for drinks. After a few hours of talking when I was really drunk, he took my hands and started repeating a mantra that we were adults and that everything that was happening was good, as he felt I liked him, and that the feeling was mutual. He tried to talk me into this, at the same time touching my hands and trying to get closer. At one point, he undressed me, and from then on it is very difficult for me to talk," said the actress, 25.
Steponaitytė said she had tried to stop the director, although did not directly pushed him away.
"It was a constant attempt to satisfy his sexual desires with my body but I did not touch him at all and did not satisfy his sexual fantasies," she told the portal.
In her words, Bartas "attempted to do the same thing again" next morning.
Steponaitytė said she planned on going to court.
Bartas, 53, is one of Lithuania's most famous directors, winning multiple prizes and the Lithuanian National Culture and Arts Prize. In 1989, he established Lithuania's first independent film studio Kinema.