And a Fairfax Media investigation can reveal  a college that had already been flagged by another government agency as being involved in education rorts was offered the opportunity to apply for the fast-tracked visa process by the Immigration Department.

Immigration offered TK Melbourne Education and Training College to apply for the expedited visa process in March, even though the Australian Skills Quality Authority had weeks earlier found the college to be in "critical non-compliance" with national standards.

Leaked documents reveal that the college has allegedly been providing fake qualifications costing tens of thousands of dollars, a practice that industry sources say is widespread and is often coupled with the exploitation of overseas workers.

The revelations come after the Australian Federal Police charged the owners of another international college, the St Stephens Institute, with serious fraud offences on Wednesday afternoon.

The federal police began a probe last November after Fairfax Media provided the AFP with evidence the college was involved in suspected criminal conduct and the exploitation of dozens of overseas workers sub-contracted to work for Australia Post.

One of the charged men who part-owns the institute, Baljit "Bobby" Singh, has been paid millions of dollars by the federal government and Australia Post, despite repeated union warnings that he was exploiting overseas students and workers.

Australia Post terminated Mr Singh's labour hire contracts on Wednesday and said it was increasing efforts to stop contractors exploiting workers. But Mr Singh remained listed as a registered training provider on the federal government's training.gov.au website as of Wednesday night.

Rakesh Kumar, 37, and Mukesh Sharma, 42, appeared before Melbourne Magistrates Court on Wednesday on five charges each, including conspiring to obtain or gain from a Commonwealth entity, possessing forged documents and dealing with money or property that is suspected of being the proceeds of crime.

Mr Kumar is also charged with falsifying documents.

Both men were granted bail to return to court in January. It is understood Mr Singh remains in custody on similar charges, but prosecutors are unlikely to oppose him being granted bail.

AFP Manager Crime Operations, Paul Osborne, said the success of this operation highlights the need for agencies to continue to work together to stop those individuals who believe they are above the law.

"In this case, the men involved have created an elaborate plan and defrauded millions of dollars in government funding and from students in vulnerable circumstances," Commander Osborne said.

"I would like to stress that the AFP would not have been able to successfully disrupt this scheme without the cooperation from Australia Post throughout this year-long investigation."

It is suspected that the St Stephens Institute was set up as a hub for recruiting and exploiting overseas workers and students who were prepared to pay large sums of money, or to forgo pay and conditions, to get visas.

The revelations raise major questions for the Immigration department, which was recently merged into Australia's new border force agency and which has previously faced fierce criticism for failing to crack down on visa rorting.

They also highlight ongoing concerns about Australia's ability to police unscrupulous education providers, employers and migration agents who sell access to temporary skilled working visas and student visas, while holding out the hope of permanent residency.

The Salvation Army on Wednesday called on the federal government to ramp up measures to prevent the exploitation of migrant workers, while unions said the Abbott government needed to "take action to stamp out these appalling practices".

TK Melbourne Education & Training College has allegedly provided overseas students with back-dated certificates of education in return for large payments.

An audit by the Australian Skills Quality Authority February found TK Melbourne to be in "critical non-compliance" with national Registered Training Organisation standards.

The following month, in March, the Immigration Department offered TK Melbourne the ability to apply for "streamlined visa processing". An Immigration spokesman said the visa offer was part of a "blanket-offer" sent to dozens of education providers and did not mean TK Melbourne would have met the criteria for approval.

The college  offers overseas students certificates in business management and early education learning, which are used to support applications for 457 and other types of visas to work in Australia.

The ASQA audit found "several occurrences of plagiarism" with "entire sentences and paragraphs" in some TK Melbourne students' work being "direct copies". This happened even when students were writing on different topics.

It also appears some TK Melbourne students have not been doing their own course work, with the same handwriting appearing in assignments from several different students' portfolios.

ASQA found the duration of training for several qualifications "was not consistent" and resulted in a "significant deviation" from national standards that could not be adequately explained.

"The amount of training has not been determined based upon the existing skills, knowledge and experience of learners, with the timeframes being insufficient to allow for new entrants into the industry sectors to effectively develop all of the skills and knowledge required," the ASQA audit found.

It also found TK Melbourne did not have proper facilities to accommodate the number of students it claimed to have on its books, with an attendance register from February stating 252 students were present when its premises could only hold 118 people at that time.

TK Melbourne also only had four trainers and assessors present to oversee its claimed 252 students. Further, four of the assessors TK Melbourne told auditors it had on its books claimed to be no longer working there.

Documents show TK Melbourne allegedly provided a foreign student a certificate to show she had completed a six-month business course on October 3 last year. However, internal TK Melbourne emails show the student had only received an "offer letter" from TK Melbourne to begin their course on October 10.

On October 15, TK Melbourne provided a "completion letter" regarding the same student's certificate III in business, which the letter claimed began in March last year and was an English-language full-time course.

The Australian Federal Police told Fairfax Media it had in March referred information about TK Melbourne's alleged provision of "fake/fraudulent educational qualifications to assist in person obtaining visas into Australia" to the Immigration department to investigate.

The AFP statement said the Immigration department had begun its investigation. But Immigration is understood to have referred TK Melbourne back to ASQA.

Through its lawyers, TK Melbourne denied involvement in providing false qualifications to students and said any compliance problems identified by ASQA could and would be rectified.

- with Adam Cooper