Education Minister Leighton Andrew has ordered English Language GCSEs sat by Welsh students to be re-graded by exam board the WJEC.
It follows concerns that the results were unfair because of a change in grading boundaries introduced mid-way through the academic year.
He has now issued a formal direction to the board, forcing it to take action.
Responding, the WJEC said they would proceed with the request but 'were concerned about a number of issues'.
Today, teachers' union NUT Cymru has supported Mr Andrew's call. Secretary of NUT Cymru, David Evans, says a re-grade is 'overdue'.
However, the chair of the exams watchdog in England has accused the Welsh Government of acting 'for political reasons' in ordering English Language GCSEs to be re-graded.
Amanda Spielman told MPs on the Education committee that WJEC results were considered to be too high compared to other exam boards.
Mr Andrews then used social networking site Twitter to reply to Ms Spielman's criticism.
Meanwhile, students at Duffryn High School in Newport said many felt 'disappointed' and 'cheated' by their results.