A group representing private colleges has threatened legal action against immigration authorities over attempts to stop economic migrants exploiting the student-visa system.
From 6 April, only colleges deemed "highly trusted" may recruit foreign students to "level-three" and sub-degree courses that include work placements.
The move was announced last month by Alan Johnson, the Home Secretary, who said these courses were "attractive to economic migrants" and should therefore only be offered by institutions with "a strong record of student compliance".
The UK Border Agency subsequently said that publicly funded institutions would automatically count as highly trusted, adding that a "rapid but rigorous system" would be developed to allow private colleges to gain the same status.
The agency has not formally clarified the criteria that private colleges must meet to join the highly trusted list, but at a meeting with the Joint Education Task Force, it said they would have to show dropout rates of less than 1 per cent in the first quarter of a course. Many publicly funded universities would not qualify on this basis.
Study UK, a membership organisation for private colleges, and English UK, which runs English language schools, said the new system was unfair. Applicants would view the private bodies as less competent, which would suffer financial losses as a result, they argued.
They said that as the criteria and timescale for joining the list had not yet been formally confirmed, they could not mitigate their losses.
Study UK has warned UKBA to postpone the introduction of the highly trusted scheme or face a judicial review on the grounds that its actions are unreasonable.
English UK is threatening a judicial review over proposed changes to requirements regarding would-be students' English-language skills.
Jeremy Oppenheim, head of the points-based visa system at UKBA, said the scheme was "designed to benefit all institutions with a proven track record of bringing in and educating legitimate students".
"To ease the transition, a number of trusted public institutions have been transferred on to the new scheme while their applications are being considered," he added.
"Private bodies have until the end of April to apply, and until a decision is made on those applications, they can continue to sponsor foreign students as they do now."
Any restriction on Study UK members' ability to recruit overseas students is likely to affect universities, which receive fees from colleges for accrediting their courses.
A report on private higher education commissioned by Universities UK and published last week says that 177 colleges accredited by the British Accreditation Council have links to 60 state-funded UK universities.
About 26,000 students are studying for UK-validated awards at BAC-accredited colleges, while dozens more colleges are accredited by the Accreditation Service for International Colleges. There are also five companies providing foundation courses to 33 universities.
The report, The growth of private and for-profit higher education providers in the UK, recommends that UUK open itself up to private bodies with degree-awarding powers. The University of Buckingham, a private institution, is already a UUK member, and admitting others would improve mutual understanding in the sector, it says.