Ministers are to tighten immigration rules in an attempt to force firms to hire unemployed British people rather than relying on overseas skilled workers.
Jacqui Smith, the Home Secretary, said British people who were out of a job should in future get the "first crack of the whip" at tens of thousands of skilled posts which fall vacant every year.
In particular, companies are to be told they must advertise vacancies in the JobCentre Plus network in Britain before filling them with skilled immigrants.
Government sources estimate that, had the planned crackdown been in force last year, between 60,000 and 80,000 posts would have been filled by Britons rather than immigrants.
Currently, employers often rely on "tier two" immigrants – those coming into the UK from outside the European Union with a job offer – to fill a range of posts including primary school teachers, some categories of nurses, architects, farm managers, hotel managers, graphic designers, air traffic controllers and construction workers.
Ministers believe the "points-based" immigration rules must now be tightened to help fight rising unemployment among British people during the economic downturn.
The jobless total rose to 1.9 million people in the three months to October, equal to six per cent of the workforce, with some experts predicting the total will hit three million before the economy recovers.
However, critics claimed that the tightening of the rules would not be effective without an annual cap on the number of non-EU migrant workers allowed into the country, as the Conservatives have proposed.
Employers are already required, under the "resident labour market test" , to try to fill vacancies from within the UK before they are permitted to recruit immigrant workers.
However, trade unions have complained that the rule is widely ignored by firms which find it cheaper or easier to take on staff from overseas.
Ms Smith and James Purnell, the Work and Pensions Secretary, are working "urgently" to develop a set of proposals which are expected to be announced within weeks.
In a closely linked move, John Denham, the Skills Secretary, is working on plans to teach new skills to thousands of British workers so they have a stronger chance of being able to get back into the job market more quickly.
The Home Office initiative, which follows Gordon Brown's "jobs summit" last week, comes as ministers become ever more aware of a rising tide of discontent among British workers that more and more skilled jobs are going to people from overseas.
Skilled workers are a key constituency whose support Labour must retain to have any hope of retaining power at the next election.
Ms Smith said: "At a time when people are worried about losing their jobs, and therefore worried about being able to get quickly back into another job, it's even more important that we can say and show that when jobs become available, it's British people who get the first crack of the whip of taking those jobs."
The resident labour market test should be strengthened, Ms Smith said. "We need to be very sure that a job is being actively marketed for a worker who is already here and who needs that job before we assume that migration is the only way we can fill those skill shortages.
"That's one of the ways we can demonstrate that the points-based system is a more flexible way of controlling immigration for the overall benefit of the country than, for example a crude cap would be."
Dominic Grieve, the shadow home secretary, said: "The points based system was only introduced five minutes ago. We warned then it would not work without an annual limit on immigration and, despite Jacqui Smith's rhetoric, this is still the case."
