Scotland's largest teaching union is to ballot its members in secondary schools on industrial action over "excessive and unsustainable" workloads.

The Educational Institute of Scotland (EIS) said the introduction of new qualifications under Curriculum for Excellence reforms alongside cuts to staff and resources had placed a "huge burden" on both teachers and pupils.

National 4 and 5 Qualifications were brought in to replace the old Standard Grades last year, with schools given the option to phase in new Higher exams this year.

The union said the decision to ballot over industrial action was backed by the EIS council today after gaining the approval of the executive.

Any action would stop short of a strike but would see teachers "working to contract" by boycotting any additional work and assessment related to the new qualifications.

The union said it would not have any wider impact on extra-curricular activities teachers may be involved in.

General secretary Larry Flanagan said: "The introduction of the new qualifications has, at times, been rushed and has also been significantly under-resourced.

"The demands placed on teachers as a result have been both excessive and unsustainable, with serious implications for teachers' health and wellbeing.

"Significant pressure has also been placed on pupils - both as the result of the changing qualifications system and due to continuing over-assessment in order to meet SQA requirements.

"The clear message that we are getting from members in the secondary sector is that enough is enough, which has resulted in today's decision to move to an industrial action ballot."

Mr Flanagan said the decision had not been taken lightly and described industrial action as a "last resort".

He added: "The reality is that despite years of discussions with the Scottish Government, local authorities and the Scottish Qualifications Authority over the desperate need to reduce the excessive workload associated with the new qualifications, too little has been done to tackle this problem.

"That is why the EIS has taken the decision to ballot its members and why we plan to launch a sustained programme of industrial action until real and lasting reductions in qualifications-related workload for pupils and teachers are delivered in secondary schools across Scotland."

A Scottish Government spokesman said: "We are working with partners, including the EIS, to consider any issues around the new qualifications, including teacher workload, and to cut unnecessary bureaucracy in schools.

"The SQA has already reduced the level of verification for the new qualifications in response to teacher feedback.

"We would urge the EIS to continue to pursue its concerns through the ongoing work of the Reflections group, which it is a member of, rather than through industrial action.

"Industrial action would not be in the interests of anyone, least of all pupils and parents."

He added the Scottish Government had provided an "unprecedented" level of support for the new qualifications, including additional funding of £11 million since 2012.

Scottish Labour's opportunity spokesman Iain Gray said the SNP's record on education was "one of broken promises and mismanagement".

He said: "The new curriculum and exams were brought in without the necessary resources. We saw the new Higher Maths shambles. We saw that enrolment and attainment in the new nationals has fallen. Now ministers have driven teachers to the edge of industrial action.

"No-one wants to see industrial action in our schools and (Education Secretary) Angela Constance must get this sorted and quickly, otherwise parents and pupils will pay the price for her incompetence, yet again."