The Conservative MP leading a parliamentary inquiry into the English Baccalaureate has warned that it will lead to middle-class pupils gaining more attention and resources "at the expense of working-class kids".
The Commons education select committee has yet to produce its report on the Coalition's EBac, but Graham Stuart, its Tory chair, aired his concerns last week.
The MP said the controversial performance measure - which requires GCSEs or IGCSEs of at least grade C in English, two sciences, maths, history or geography and a language - would, like other indicators, lead to schools focusing on particular pupils to improve their scores.
"I think we are creating another artificial divide which ... if you compare it with the five good GCSEs (measure) is in fact going to be a higher bar," Mr Stuart said.
"It therefore means that the borderline students who will get most of the attention of the leaders in institutions will in fact be more academically able and more likely to be middle class.
"It could be argued that it in fact will lead to a greater focus of attention, resource and input on middle classes at the expense of working-class kids."
Mr Stuart's comments are his second public criticism of the EBac. In April, in an article written while his inquiry was still taking evidence on the measure, he warned that it could mean "little room" for subjects like music, and provision for less able pupils being "dismantled".
The MP was speaking at a Cambridge Assessment seminar last week, where he also said he doubted that it would become the norm for most pupils in the "poorest and most deprived schools" to achieve an EBac.
Mr Stuart is only the latest figure to challenge ministers' expectation that every pupil should achieve the measure.
Last week Matt Grist, senior researcher at think-tank Demos, told The TES: "The EBac is so hard I can't see it going above 35 per cent (of pupils achieving it) except maybe in large areas of upper-middle class kids."
Sir Michael Wilshaw, head of Mossbourne Academy in Hackney, east London, who has been feted by ministers, has called for the inclusion of a "technical and craft-based curriculum option" because there will always be pupils "for whom an academic curriculum is not appropriate".
Just 15.6 per cent of pupils achieved an EBac last year. But that figure was based on GCSEs sat before schools were told they were to be judged on the measure.
A Department for Education spokesman said: "The English Baccalaureate will encourage all schools, not just those in affluent areas, to offer their pupils the opportunity to study a core of academic subjects that top universities say they want.
"But it is just one measure of attainment. We have also introduced a progress measure and maintained the main standard measure of five good passes, including English and maths."