Teaching unions have urged the Assembly government to abandon its plans to cut training by two days a year, warning that the move would undermine the introduction of the new school effectiveness framework (SEF).
Unions say that if education minister Leighton Andrews reduced the number of inset days from seven to five, it would put fresh pressure on classroom teachers.
They said they were also alarmed that CPD opportunities have already been reduced by a recent 30 per cent cut in the Better Schools Fund and the scrapping of the individual CPD programme run by the General Teaching Council for Wales.
Union officials have demanded the extra days are retained to help teachers prepare for the introduction of the SEF, which is being rolled out across all schools in Wales from September.
Rex Phillips, Wales organiser of the NASUWT, said: "When does the minister expect that work to be done because clearly it won't be done in the teacher's own time?
"Are they going to cram everything in to the five days? It won't work; it will put a great deal of pressure on teachers."
Dr Philip Dixon, director of ATL Cymru, agreed. "We are going to see the introduction of SEF, changes in the curriculum bedding down, the introduction of professional learning communities and most importantly there's no money for CPD," he said.
"This move will curtail what little CPD and enhancement time there is for teachers. It seems short-sighted when GTCW money has been cut."
Elaine Edwards, secretary of Welsh-medium union UCAC, said: "We support the need to keep the extra two days because of the extreme difficulty of people being released from schools to access CPD opportunities."
The extra two inset days were originally put in place in 2006 to support key stage 23 transition, early preparations for the revised 2008 school curriculum and development of the 14-to-19 agenda.
They have been retained to help with developments, including the phased implementation of the play-led foundation phase for three-to-seven year olds, the revised school curriculum for seven-to-19 year olds, the ongoing roll-out of revised assessment arrangements for seven-to-14 year olds, and work around 14-to-19 developments.
An Assembly government spokeswoman said: "The education minister is considering this matter. No decision has been made yet.
"The minister recognises the need for the continuing professional development of school staff, but is conscious also of the importance of schools being open for the business of teaching and learning.
"The minister is very conscious that parents and pupils were concerned at the loss of teaching time when schools closed due to bad weather earlier in the year."