The demand being made by the Welsh education schools group, Cymdeithas Ysgolion Dros Addysg Gymraeg (Cydag).
It highlights severe delays in publishing Welsh language textbooks, with examples of teachers giving up summer holidays to translate.
The Welsh Government said it was "committed" to Welsh-medium resources.
But Cydag, which represents about 57 Welsh-medium schools, has voiced their concerns in a letter to the education secretary Kirsty Williams.
The body told BBC Wales' Newyddion 9 that it wanted "principled" Welsh Government decisions and called the current situation a "crisis."
Cydag secretary Arwel George said: "We see documents and policies which state that the Welsh Government intends to treat both languages equally and encourage more pupils to study through the medium of Welsh.
"The implementation of policies falls very short of this."
Nine new GSCE and six A level courses will be introduced in 2017, yet only two have so far been approved by the regulator, Qualifications Wales.
Cydag claims any delay will give the examining board, WJEC, little time to prepare Welsh language resources.
"Qualifications Wales and WJEC are working closely together in the development of specifications and sample assessment materials for those subjects planned for first teaching in September 2017," a spokesperson for Qualifications Wales said.
"The process is on schedule and draft specifications are available in all subjects bilingually. We currently expect final approved materials to be available in line with the schedule published on our website."
"We are absolutely committed to getting the right resources available to support teaching and learning through the medium of Welsh," stated a Welsh Government official.
"That is why we invest over Â£2.6m annually in developing and publishing Welsh-medium resources across all curriculum and vocational subjects for 3-19 year olds.
"We understand the challenge in getting texts by commercial publishers translated.
"We expect WJEC to work with publishers to make sure that this process continues to improve."
New GCSE and A Level courses in Wales should not be introduced next year unless English and Welsh textbooks are published simultaneously.