National Education Union Cymru said the Welsh government had taken initial steps to stop people being put off a career in the classroom, but more needed to be done.
New data, compiled by the BBC using Welsh government statistics, reveal that the number of teaching job adverts placed in Wales has outstripped the numbers of applicants over the past decade.
Since 2007, the number of adverts has risen by 9.4 per cent but the number of applicants dropped by 18.6 per cent. At least 14 teaching jobs advertised last year failed to attract any applicants.
Owen Hathway, Wales policy officer at the National Education Union Cymru, said: “There is no doubt that rising workloads, cuts to teachers’ pay and pensions, and the pressure put on the role are making it more and more difficult to recruit and retain teachers.
“We are not in a crisis situation in Wales but certainly, if we do not do more to respond to the concern of teacher workloads, and raise the esteem of the teaching profession, then the ingredients are there for such a crisis to occur.”
But the Welsh government said the teacher vacancy rate was comparatively low.
“We know that there can sometimes be local difficulties in recruiting in certain subjects or phase,” said a spokesman.
The figures showed jobs teaching physical education attracted the most applicants per job, an average of just under-16. The subjects with the least applicants per job were Welsh as a first language (3.5), chemistry (4.1), biology (4.5), and physics (4.6).
Mr Hathway stated: “The Education Workforce Survey, published this year, showed that a significant number of the profession are considering leaving teaching in the next few years.
“We also know that recruitment levels, especially in the secondary sector and with regards to specific subjects like Welsh and the sciences, continue to prove challenging.”
The Welsh government spokesman added: “In recent years, we have targeted the highest levels of support toward attracting top graduates with high levels of degree subject knowledge in the secondary designated priority recruitment subjects of mathematics, chemistry, physics, Welsh, foreign languages and computer sciences.”
The Welsh government has also introduced a new incentive scheme to attract bilingual teachers (Wales plans cash incentives to boost teacher recruitment, SecEd, November 2017: http://bit.ly/2zj0dc2 ).