Teaching unions have questioned the legality of an announcement by Education Minister Peter Weir that schools should reopen on August 17.
Addressing hundreds of head teachers in an online broadcast hosted by the National Association of Head Teachers (NAHT), Mr Weir said pupils in primary seven and those taking their GCSE and A-levels in years 12 and 14 should be back at school by that date.
This is the first time Mr Weir has set a date, having previously said some years would return in August with the rest to be phased in from September with a mix of classroom and remote learning.
Asked during the meeting how the date would affect school holidays, Mr Weir said: "I think the aim would be to have every school open at that stage in the same way as the same position in other jurisdictions as well.
"I'm not quite sure at the moment where anybody's going to be going on holiday on August 17."
Mr Weir added that not all school staff would be required to start back on this date, given the limited numbers.
The Ulster Teachers' Union have already called for legal clarification on Mr Weir's remarks.
"We were previously assured by DE (the Department or Education) that attendance from August 17 would be voluntary on the part of schools and teachers," said the union's General Secretary Jacquie White.
"However, it now appears that directions have been issued by the Education Minister, to principals in a recent webinar.
"This raises significant questions around the implications on teachers' contracts and any holidays booked.
"We would emphasise that schools should not be acting upon such directions and should wait until further official guidance is published as the legal basis with regard to that matter remains unclear.
"We will continue to engage with the relevant authorities to get clarification as a matter of urgency, to ensure new arrangements won't conflict with teachers' contractual rights."
Dr Graham Gault, vice-president of the NAHT in Northern Ireland, told the BBC: "We have no clarification on what the contractual arrangements are going to be for the staff, none whatsoever.
"And the minister would be very well advised to talk fully with the trade union bodies as soon as possible to have that all ironed out.
"That can't be left for a principal to be making those decisions on behalf of staff and it also can't be left to be voluntary.
"Clear guidance needs to come from the minister as soon as possible."
A spokesperson for the Department of Education said it fully appreciated the "legitimate concerns" from teachers, parents and pupils and that there were still a range of "highly complex" issues that needed to be addressed.
The statement added the opening would be subject to medical and scientific advice, and most pupils will have a mix of classroom and remote learning.
The spokesperson said: "It is clear that the longer that children are out of school full-time, the more it prejudices their long term educational prospects. Therefore the aim remains a return to full-time classroom education as soon as medical guidance allows this."
The department has now established a Restart Programme, with both the minister and the department set to consult with a wide range of stakeholders.