Details of the internal government documents, obtained through an Access to Information request, were shared by the group in a news conference Friday morning in Calgary.
The organization says the documents show the Harper government sanctioned the underpaying of thousands of temporary foreign workers by Alberta businesses last year through the Temporary Foreign Worker Program (TFWP). Many of them worked as nurse aides, front desk clerks, truck drivers, service station attendants and heavy equipment operators, among other vocations.
"It's pretty clear that the problems in the Temporary Foreign Worker Program extend far beyond the food services industry," said Gil McGowan, president of the Alberta Federation of Labour. "Canadians should be appalled by the picture that's painted by these documents."
McGowan says the documents show 3,718 individual low-skille foreign worker positions were approved in Canada last year.
Of those permits, 2,122 of them were issued to employers in Alberta.
For part of 2013, the TFWP allowed employers to pay foreign workers five to 15 per cent less than the prevailing wage in the sector. That was changed partly through the year, making it illegal to pay them less than what a Canadian would earn in the same position.
McGowan would not say how many of the thousands of cases they highlighted Friday morning took place during the time when underpaying foreign workers were legal and how many took place after the practice was banned.
For that reason, it's not clear at this point how many temporary foreign workers may have been illegally underpaid.
Changes likely to be reversed, McGowan says
The federal government again revamped the program in June 2014 after an investigation that followed a CBC News series on alleged misuse of the program by fast-food outlets.
Employers were barred from hiring foreign workers in regions where unemployment is high and received a cap on the number of foreign workers they can hire.
The new rules also brought in a more stringent screening process for employers to prove they need to hire a foreign worker over a Canadian one, and also increased the number of spot checks in the workplace and fines for those who break the rules.
Alberta has since begun pushing Ottawa for more provincial control over the program.
If pressure continues to build from Alberta and businesses, McGowan says he expects the federal government will cave and reverse its changes to the program.
"We are afraid the government, which is after all a business-friendly government, is going to cave in to business pressure," he said. "These documents are a red flag."
Alberta has repeatedly struggled with a labour shortage in low-skilled and high-turnover industries, including fast food and retail.
The availability of high-paying work in the oilsands makes it hard for those industries to retain workers, and it's estimated the oilsands alone will require more than 25,000 new workers over the next 10 years.