Bus Éireann has said it is within Department of Transport guidelines in using a 53-seater bus to accommodate 71 children in Co Leitrim.
The State company was reacting to concerns of teachers and parents of children at Annaduff national school after being informed that two school bus routes would remain amalgamated into one. The routes have been amalgamated since last Monday as part of a national review of the school bus service.
It means that where 71 children were being brought to Annaduff school on two buses, they are now transported on one.
Parents are "very concerned" that their children's safety may be at risk, said the principal, Mr Vincent Tighe.
"It means they are having to all squash in three to a seat and it just does not seem safe. Some parents I know have stopped letting their children go on the bus and are having to drop them up to the school themselves."
A spokesman for Bus Éireann said a review of the school bus network meant there were amalgamations of routes across the State.
"But there have been no other complaints about these made to the company, as far as I am aware," he said.
The chairman of Leitrim County Council, Cllr Seán McGowan (FF), will table a motion at the next council meeting calling on the Department of Education to introduce legislation ensuring all children travelling on school buses must wear seat belts and to restrict numbers travelling on buses.
A spokeswoman for the Department, however, said Department of Transport guidelines allowed three pupils to every two-seater seat on a school bus.
"This means a 53-seater bus can accommodate 79 pupils," she said.