Music and drama could become the "preserve of the elite" as a result of a drive for teenagers to take traditional academic subjects at GCSE level, school leaders have warned.
Under Government proposals, most pupils in England could be required to take subjects included in the English Baccalaureate (EBacc) in the future.
But the move could mean that creative subjects are squeezed out of the curriculum, according to the Association of School and College Leaders (ASCL), which said it would be a tragedy if schools were forced to axe these courses.
Millions of pounds has been pumped into arts education and the numbers taking these subjects at GCSE is rising, the Department for Education (DfE) argued.
The union said it had calculated that the EBacc, plus other curriculum requirements, would leave just 20% of a student's time for creative and technology courses, which could restrict the number of options they are able to take.
There are concerns that this will lead to a decline in student numbers for these GCSEs, and make some unsustainable, ASCL said.
Music and drama are particularly at risk because uptake for these courses is already lower than for many others, it added.
Macolm Trobe, ASCL's interim general secretary said: "It would be a tragedy if an unintended consequence of EBacc is that it becomes impossible for schools to run music and drama courses.
"The danger is that these subjects will then end up becoming the preserve of the elite, accessible only to those who can afford private tuition.
"We agree with the Government that learning core academic subjects is crucial to the future of young people. We think that the EBacc needs to be more flexible to leave room for creative and technology subjects.
"These subjects are important for young people and for the economy. Creative industries alone are worth nearly £80 billion a year to the UK and account for 1.7 million jobs."
The Government has said that by 2020, it wants at least 90% of pupils in England to be taking seven GCSEs in EBacc subjects - including English, maths, two science subjects, history or geography and a language.
Education Secretary Nicky Morgan has previously argued that every child should study a "strong academic core" up to age 16 and that these subjects are the "foundations of a good education that will ultimately keep options open for young people's future".
Arts subjects are compulsory part of the national curriculum up to age 14, the DfE said, adding that the numbers of teenagers taking an arts GCSE has risen from 45% in 2010 to 49% in 2015.
Last year, 38.7% of pupils in state schools were entered for the EBacc, compared to 21.8% in 2010.
A DfE spokeswoman said: "ASCL aren't just being disingenuous, they are ignoring the facts. All young people should study the core academic subjects that give them the skills to succeed but it is a myth to suggest this must come at the expense of the arts.
"Last summer's results showed thousands more students taking GCSEs in arts or music subjects compared to the previous year and the percentage of pupils in state-funded schools with at least one arts GCSE has increased since the EBacc was introduced.
"The arts are a key component of the broad and balanced education we expect all pupils to receive and this Government has invested millions in arts projects, including schemes to help talented musicians and dancers from all backgrounds attend world-class institutions like the Royal Ballet School."