"We remain committed to protecting the integrity of the immigration system," Citizenship and Immigration Canada spokeswoman Melanie Carkner told AFP.
Offering amnesty "would encourage illegal immigration and it's unfair to the hundreds of thousands of people who applied through legal channels and have waited patiently," she said.
Andy Manahan of Universal Workers Union Local 183 lamented the decision, saying it "is short-sighted" and could have "a great negative economic impact" on Canada's booming construction sector, which relies on foreign workers.
Unions, home builders' associations and community groups, which represent thousands of undocumented trade workers, have lobbied for an amnesty, pressing five different immigration ministers in six years for changes, but to no avail.
"We're looking for ways to make it easier for trades people and people who don't necessarily have a university degree to come here ... But, we're not going to allow people to jump the queue," Immigration Minister Monte Solberg told Parliament on Friday.
Many of the illegal workers are from Portugal, Argentina and El Salvador, according to reports.
"Canada's current immigration system favours academic qualifications and English language proficiency. It is biased, favouring white collar workers over trade workers," Manahan told AFP. "It needs to be reformed."
He wrote to Solberg in August asking to set up a pilot program to legalise undocumented workers' status.
"If you look at the history of construction in Canada, there has been waves and waves of immigrants who didn't speak English, but many eventually became quite successful," he said.
In a reply, obtained by AFP, an immigration official said Solberg understands the difficulty and vulnerability of people working illegally in Canada and would ensure that "Canada's immigration policy is reoriented to meet the demands of our labour market."
But, Canada must also maintain its policies to "drive foreign workers to legal channels," the official wrote.
"Even a small increase in the number who decide to come here and stay here illegally based on the hope of regularisation would simply recreate the very problem the (amnesty) proposal is supposed to fix."
In March, Portuguese Foreign Minister Diogo Freitas do Amaral made an urgent trip to Ottawa to investigate claims that Canada planned to deport thousands of Portuguese nationals.
The expulsion of several families working illegally in Canada, mainly in service sector jobs, made headlines in Portugal, a nation with a long history of emigration.
Portuguese immigrants' groups alleged Canada's Conservative government, elected in January, was applying immigration laws more harshly, showing no tolerance for illegal immigrants and had specifically targeted immigrants from Portugal.
Solberg denied the allegations, saying Canada has "probably the most generous immigration system in the world."
Freitas do Amaral also said he received assurances from Canada's immigration and foreign ministers that Canada had no plans for mass expulsions.
Officials told AFP then that Canada expected to deport 11,000 people this year, which is in line with the rate of the two previous years. About 190 people were deported to Portugal last year.

Copyright AFP (Agence France-Presse), 2006