The exams watchdog needs to investigate whether qualifications deserve the value given to them by school league tables, according to England's biggest exam board.
The Assessment and Qualifications Alliance (AQA) is "concerned" that Ofqual is not checking whether qualifications deemed to be equivalent in performance tables are actually of equal worth.
Bill Alexander, the board's curriculum and assessment director, said: "The question is, 'Is a C in an alternative qualification really worth the same as a C at GCSE?' We want to open up that debate."
Ofsted made a similar recommendation in a report on secondary science last month that called on the Government and Ofqual to "ensure that rigour and equivalence are preserved across the many different science qualifications".
Equivalence has been a big issue ever since large numbers of schools began to offer ICT GNVQs in a phenomenon that critics said had more to do with climbing league tables than educating pupils. The vocational qualification, now phased out, was judged to be worth the equivalent of four A*-C GCSEs despite needing a fraction of the teaching time.
Since then, schools have switched to two new ICT vocational qualifications deemed by Ofsted to be of "doubtful value".
They also require much less teaching time than GCSEs, leading many to suspect a new league table ploy from schools.
AQA's intervention comes soon after ministers gave the go-ahead for another qualification to be added to the GCSE league table mix - the O level-style IGCSE.
Mr Alexander said it was important that Ofqual assessed the worth of the more traditional-style exam in relation to conventional GCSEs.
"There is a view being put out there that they (IGCSEs) are much more challenging than GCSEs, but there is no research to substantiate that," he said.
AQA is the biggest provider of GCSEs and, unlike its two big rivals, does not currently offer the IGCSE or any other qualification deemed equivalent to GCSEs in the league tables, apart from the Diploma.
The board's stance first emerged in its response to Ofqual's consultation on how it should regulate.
"While it is central to the remit of the regulator to ensure consistency of standards within any one family of qualifications, it is also essential to ensure the equivalence of qualifications which have equal value in performance tables or in selection processes," the board said.
"It is of great concern to AQA that there is little mention of such equivalence in the draft regulatory proposals."
The Government is working on the detail of its forthcoming proposals for league table reform.
An Ofqual spokesman said it would take AQA's points into account when it conducted more detailed consultations on its role.