Reluctant witnesses, scant evidence, and limited time and resources pose serious challenges when it comes to investigating crooked immigration consultants, the Canada Border Services Agency says.

Agency president Luc Portelance tells Public Safety Minister Steven Blaney in a newly disclosed memo that fraudulent activities involving unscrupulous consultants "threaten the integrity of Canada's immigration program."

The correspondence highlights the latest headaches confronting federal officials in their long battle against criminals who take advantage of people desperate to come to Canada.

The memo, released under the Access to Information Act, says the border agency has received more than 700 referrals of suspected consultant-related fraud for criminal investigation since 2008.

About 140 of these have resulted in investigations.

Over the last six years, the Public Prosecution Service of Canada has accepted 22 cases, with 13 resulting in guilty convictions and several others still making their way through the courts, the memo adds.

Obtaining evidence of fraud 'continues to be a challenge': memo

In 2013-14, the border agency opened 40 investigations into consultant fraud — the highest number in the last six years.

"Most of these cases are still under active investigation," the memo says.

However, consultant fraud cases are among the most time-consuming and resource-intensive investigations, Portelance notes.

In August the border agency laid four charges against an Edmonton consultant who allegedly provided her clients with forged documents — charges that came three years after the agency received a complaint against her.

Obtaining evidence to prove intent of a crime often includes several search warrants, production orders, interviews and surveillance operations, Portelance says in the memo.

"The focus on complex cases creates a significant pressure on (border agency) time and resources, and statistical reporting often does not truly demonstrate the significant amount of work being undertaken at a given time," it says.

"Additionally, obtaining evidence of consultant fraud continues to be a challenge."

Applicants 'often hesitant' to report fraud

Immigration applicants are "often hesitant" to report consultants, as they were either complicit in the misrepresentations or they remain convinced their consultant can help them gain status in Canada, Portelance says.

"Many applicants fear removal from Canada as they did not acknowledge using a representative for a fee or consideration."

In addition, contracts between shady consultants and prospective newcomers are often verbal — with payments made in cash — leaving little documentary evidence for use in court.

Portelance suggests creating a ticketing-type offence for "non-complex and low-priority cases" that do not warrant full prosecution.

Such cases might involve providing or advertising immigration advice for a fee without authorization.

However, he says, this would require consultation with federal and provincial players and amendments to immigration law.

The agency is using its intelligence-gathering and analysis to better understand the problem, as well as working closely with partners including Citizenship and Immigration Canada and the Immigration Consultants of Canada Regulatory Council, Portelance adds.

Priorities for the agency's 200 criminal investigators include consultant fraud, human smuggling, marriages of convenience, export violations, weapons and tobacco smuggling, commercial trade fraud, and food, plant and animal offences, the memo reveals.

The aim is to tackle high-risk offences that will "have the greatest impact on the nation's economic and social well-being."