A mass exodus of temporary foreign workers is on the horizon, employers and lawyers predict.

Beginning April 1, low-skill, temporary foreign workers who have been in Canada at least four years will be forced to leave.

Most of those workers are employed in the agricultural and fishing industries.

Frankly, it's a crisis. - Bill Stevens, Mushroom Canada

Bill Stevens, the CEO of Mushroom Canada, is pushing for a reprieve.

"Frankly, it's crisis with us because we're losing workers who don't want to leave, who have proven themselves to be valuable, and deserve an opportunity to apply for citizenship," Stevens said.

Stevens says the $900-million mushroom industry relies on temporary foreign workers to do jobs it can't fill with Canadian citizens.

He says Highline Mushrooms in Kingsville, Ont., and Rol-Land Farms near Blenheim are both facing major decreases in production, if the deadline is upheld.

"The whole thing amounts to a major decrease in the production of our commodity, and they're going to suffer from it, they're going to lose markets, and especially now when the markets are really very strong," Stevens said.

Stevens is pushing for a moratorium on the April deadline and for new avenues for low skill temporary foreign workers to achieve permanent residency.

Immigration lawyer Maria Fernandes in Windsor, Ont., is pushing for similar changes.

"I would like to see a reprieve, give these people two more years so we can create a program that leads to permanent residency," she said. "Workers are coming in and asking for permanent residency. The federal government wants people to obtain permanent residency, which makes sense.

"In Ontario we don’t have a mechanism to allow them to obtain permanent residency."

Under the old rules, which were changed in 2011, workers could simply reapply to continue working for their Canadian employer, Fernandes said.

Now, after a temporary foreign worker has reached their four-year cumulative duration limit, they will not be granted another work permit in Canada for an additional four years. After that time has elapsed, the worker will again be permitted to work in Canada.

Fernandes said she has one client who has worked 17 years in Canada and must now leave for four years before being able to apply again.

Reprieve given in Alberta

Some temporary foreign workers in Alberta are getting more time to become permanent residents as they face the April 1 deadline for leaving the country.

The transitional measure will offer a reprieve to some employees in Alberta working in the Temporary Foreign Worker Program as they wait for their permanent residence applications to be processed, Employment Minister Jason Kenney said in a letter to Conservative MPs obtained by CBC News.

No similar reprieve has been granted to temporary foreign workers in Ontario

"This is yet another example of the Harper government telling Canadians one thing and then turning around and doing something else to employers," Alberta Federation of Labour president Gil McGowan said.

McGowan said this new plan from the federal government is particularly "cynical, sneaky and mean-spirited" because they have tried to dress it up as an act of kindness to the thousands of TFWs who face the prospect of deportation as soon as April 1.

"This isn't an act of kindness towards anxious TFWs; it's all about making it possible for low-wage employers to hold on to more easily exploitable TFWs for another year," said McGowan.

Fernandes said temporary foreign workers work at fisheries, on farms and as ethnic cooks - all jobs she said Canadians don't want.

"The temporary foreign workers we’re talking about are doing jobs Canadians don’t want to do," she said.

Fernandes claims employers tell her there is a very high turnover of Canadian employees in those types of jobs.

She also claims a higher wage isn't the solution and that by allowing temporary foreign workers to stay, it increases productivity at the businesses and creates spinoff jobs.