The Marxist JVP legislator Anura Kumara Dissanayake said as many as 13 petitions have been filed in the Matale magistrate court.
"This is a mass grave where large numbers (of people) have been buried so there has to be an investigation," Dissanayake said.
The JVP claims the victims were their cadres who had been killed in a brutal government crackdown against them during 1987-90.
The magistrate ordered that statements be recorded from relatives and a further hearing of the case would be made on May 10.
President Mahinda Rajapaksa in April appointed a three-member probe panel on the mass grave.