The results - which are being sent out to almost 58,000 students today - show a continued drop in grades in maths and science. 10% of students failed the ordinary level papers in maths.
IBEC said continuing plans to reform second-level maths curriculum must be adequately funded and receive the full support of the education system.
The group's head of education policy Tony Donohoe said fluency in maths was vital to the educational and economic well-being of the country.
'Less than 16% of the 51,991 students that sat Leaving Certificate maths took the higher level paper. This is down from a high of 18.9% in 2005 and is significantly out of line with other subjects,' he said.
Mr Donohoe said the roll-out of Project Maths was a step in the right direction, but the quality of teaching was 'critical'.