Bus Eireann has had to issue temporary tickets to thousands of school students after problems emerged with a new computer system.
The families of an estimated 115,000 primary and secondary students have paid up to €650 for an annual school transport ticket.
But only 82,000 have actually been issued.
Bus Eireann changed the system to a computerised one this year and this changeover is now being blamed for the current delay.
Temporary tickets are being issued to families by email as the new school term starts this week.
Families are also being advised that evidence of payment will also be accepted on buses for this week until the remaining tickets have all been issued.