More than 2000 students face ejection from the UK after the Government revoked London Metropolitan University's highly trusted status (HTS) for sponsoring international students.
More than one-quarter of a sample of students there did not even have permission to stay in the country.
Professor Eric Thomas, Universities UK president, said there were other ways to address the concerns.
Sally Hunt, University and College Union general secretary, said: "The message the UK deports foreign students will reach all corners of the globe."
Universities Minister David Willetts said a task force would be formed to help overseas students.
Immigration Minister Damian Green said it was "not an option" to allow the situation to continue.
Of 101 sample cases, 26 were studying between last December and May this year while holding no leave to remain in the UK.
There was no proof students were turning up to lectures in 57% of sampled records. And 20 of 50 files checked since May for evidence of English language testing and academic qualifications showed poor assessment where documents were not verified or not held.
University vice-chancellor Professor Malcolm Gillies disputed the claims.
Last year, Glasgow Caledonian University had its licence to sponsor foreign students suspended after a check revealed irregularities among students enrolled on a nursing degree. It later had its licence reinstated. All Scots universities are compliant with UKBA rules.
Several Scottish colleges are also facing a lengthy ban after concerns over higher numbers of drop-outs than acceptable.