The Tamil National Alliance (TNA) said the government's promise that the civilians would be allowed to return to their homes had not been kept.
"There are over 3,000 families who are literally living under trees because the military is either occupying their homes or not allowing them to return to their original villages," TNA lawmaker Suresh Premachandran said.
Official figures show more than 300,000 Tamils civilians were held in internment camps when fighting ended in May last year.
They were granted freedom late last year after intense international pressure on Colombo.
Premachandran said his party had collected details of at least 3,000 families who were allowed out of the state-run camps but could not go back to their homes.
Soldiers "chased back" the civilians when they tried to return to their villages in the northern region of Wanni, Premachandran said.
"The army won the war (against the Tigers), but they can't behave like this," Premachandran told reporters in Colom