Some 350 international students at a private London business college have been told they must leave the UK by the end of next month.
London School of Business and Finance (LSBF) has had its permission to recruit and teach non-EU students revoked, the Home Office has confirmed.
One student said he feared he would be unable to complete his £8,500 course.
The college said it would intensify teaching to ensure all students gained their qualifications in time.
"These are genuine and good students," said LSBF rector and chief executive Prof Maurits van Rooijen.
"We will deal with every student on an individual basis to ensure they will be able to continue their courses and complete their qualifications."
One student studying for a master's degree in business administration at LSBF said almost half the students on his course had so far received a Home Office "notice of curtailment".
"I paid £8,500 up front, which is a lot of money in Africa," said the student, who asked not to be named.
"I did not expect this to happen in Europe and in the UK particularly.
"No-one at the college will address the question properly.
"At this time they are offering to compress the schedule so that we can finish the course by the end of March, but we are not sure this is possible."
The Home Office notice tells students their records have been checked "and there is no evidence that you have made a fresh application for entry clearance, leave to enter or leave to remain in the United Kingdom in any capacity".
"It is not considered that the circumstances in your case are such that discretion should be exercised in your favour," it says.
"The secretary of state has therefore decided to curtail your leave to enter or remain."
The students are asked to return their residence permits and told they may not work in the UK.
The Home Office said the college had been found to be in breach of its duties in sponsoring students from outside the European Union.
The college said the issue stemmed from "a technical discussion" about the proportion of non-EU students it had accepted whose visa applications had then been refused.
Government rules stipulate a refusal rate of less than 10% in any 12-month period.
Prof Van Rooijen said the college's own independently audited figures were "definitely within the margins" so it was "surprised and shocked" by the Home Office's conclusion.
He said most of the affected students, some 280, were taking professional qualifications, such as accountancy.
Most of the others were either in the final year of an undergraduate degree or on one-year master's programmes, he said.
"Almost all are near the end of their courses," he said, so it should be possible to accelerate their programmes to finish by the end of March.
The four or five students on longer courses would have to move to one of LSBF's sister institutions in France or Italy, said Prof Van Rooijen.
He said the college had been in touch with accrediting institutions to ensure changes to teaching and exam timetables would not prevent students qualifying.
The National Union of Students said the college's plans to "squash" courses into a shorter timeframe or to move students to institutions in France or Italy were not good enough and called for better protection for international students facing course changes and closures.
NUS spokesman Mostafa Rajaai said international students too often faced "unfair and unjust treatment".
"The government cannot treat international students the way it does and expect the UK to remain a desirable destination for prospective students," said Mr Rajaai.
The college is part of for-profit education group Global University Systems, which runs several institutions in the UK, Asia and North America.