"Harper is giving a go-ahead to employers to tap into vulnerable foreign workers to drive down Canadian wages," said Jim Stanford, head economist for the Canadian Auto Workers.
A federal spokeswoman said the measures, which allow workers to be paid less than the going Canadian wage, would not disadvantage workers in hot labour markets.
"Regional differences will be taken into account," said Alyson Queen of Human Resources and Skills Development Canada.
On Wednesday, the federal government said it would speed up approval times for companies to get skilled workers into Canada if local labour can't be found. It also promised better protections for such workers once they're in the country.
But it also said employers would be allowed to pay foreign workers up to 15 per cent less than the prevailing local wage.
Because foreign workers in union shops must be paid the negotiated wage, Gil McGowan of the Alberta Federation of Labour said the provision gives non-union contractors the ability to undercut union contractors.
"What happened yesterday is really about giving non-union construction contractors the upper hand in bidding for work in the oilsands sector," he said.
About half the construction work in Alberta already goes to non-union shops, McGowan said.
He also suggested that increasing the flow of skilled workers from other countries will reduce the need for employers to spend money on training and apprenticeships for Canadians.
Ron Genereux, vice-president of construction for Suncor Energy, said the wage provisions would only potentially apply to a very small number of workers. He said more than 90 per cent of oilsands construction already goes to unionized employees.
The reforms are necessary, he added.
"It was taking us six to nine months to get people here. A project duration is typically 24 to 36 months. If you waste 10 months of that 30 months, you're creating major schedule (problems) and resulting cost challenges on your project."
Employers have no cost incentive to hire from outside Canada, he said.
"Foreign workers are the most expensive workers we've got."
Queen said Ottawa will monitor local labour conditions to make sure proposed wages aren't artificially low. She also said having fewer staff processing applications means more resources will be available for monitoring and enforcement.
She noted the new measures contain provisions for on-site visits from inspectors and the power to compel records, with the co-operation of provincial governments.
Both McGowan and Stanford doubt the government's ability to determine a fair wage in a volatile economy such as Alberta's.
"For years now, people at Statistics Canada have said they don't have adequate labour market information to make this program work," said McGowan. "With the deep cuts to StatsCan, it's going to be even more difficult for them to figure out what exactly is the prevailing wage."
Stanford said all Canadian workers are threatened by the new program, not just labourers in the oilsands.
"These measures that were announced (Wednesday) will be used to staff hotels in Ontario. They'll be used for light manufacturing in British Columbia. This is part of a national low-wage strategy."
Andrew Jackson, an economist for the Canadian Labour Congress, suggested the government would have been better off to focus on coming reforms to immigration legislation that will speed applications from those with in-demand skills.
"A lot of employers would rather have an immigration system that responds more quickly," he said. "It's puzzling and disturbing to me that (the government) is expanding this back-door channel."