The requirement for new nursery staff in England to have good GCSE passes in English and maths will lead to "catastrophic" staff shortages and should be scrapped, campaigners say.
New recruits to key jobs must have at least GCSE C grades in the subjects, with alternative equivalent qualifications no longer accepted.
The Save our Early Years campaign says recruitment has already been hit.
But the government says numeracy and literacy skills are "essential".
Under the current rules, staff are only allowed to look after specific numbers of children.
- One-year-olds and younger - one member of staff to three children
- Two-year-olds - one member of staff to four children
- Three- and four-year-olds - one member of staff to eight children or one to 13 if the group is teacher-led.
Although nurseries are still able to hire staff without good GCSEs, these staff will not count towards the ratios.
The rule change applies to people who started training in 2014 or later, who nurseries hope will fill vacancies in the new academic year in September.
Save our Early Years fears many will not have managed to achieve good enough GCSE grades, despite completing their childcare qualifications, leading to a shortage of qualified staff.
Carol Medcalf, the managing director of an award-winning nursery in north London, who supports the campaign, called the rule "a huge barrier".
"I strongly feel, and this is backed up by experience, that the GCSE requirement, especially in maths, is a huge barrier for many wonderful staff entering the profession, and they become unemployable, which is crazy", said Ms Medcalf who runs Carol Jane Montessori Nursery in Enfield.
"I myself do not have maths GCSE - yet I have run a highly respected, multi-award winning, Ofsted outstanding nursery for over 25 years, and I manage to get the business figures right."
The campaigners say the recruitment crisis will be particularly acute with the government having promised 30 hours of free childcare for three- and four-year-olds from next year.
They want the government to reinstate "Functional Skills" qualifications as a suitable alternative to GCSE for childcare staff.
These qualifications are offered to the 40% of teenagers who do not achieve the benchmark English and maths GCSEs in school and are the equivalent C grades.
Julie Hyde, executive director of the childcare qualifications awarding body CACHE, said childcare was the only sector where they were not accepted.
"We simply want a level playing field," she said.
Liz Bayram, chief executive of the Professional Association for Childcare and Early Years, said feedback from members suggested trainees were being prevented from fulfilling their potential.
While Neil Leitch, chief executive of the Pre-School Learning Alliance, said he did not believe staff needed GCSEs to demonstrate they were literate and numerate.
"We simply cannot afford to be blocking smart, eager and passionate potential practitioners from joining the sector, just because they don't have the right type of qualification," he said.
A Department for Education spokesman did not directly address warnings of staff shortages, but said strong numeracy and literacy skills were "essential" for staff working with young children.
"That is why we introduced GCSE requirements for those early years staff working for 'level three early years educator' status.
"We are continuing to look at what more can be done to encourage talented staff to forge a career in the early years."