New immigration controls detailed today would have prevented 20,000 foreign workers taking jobs in Britain last year, the Home Office said.
The restrictions form part of the Government's point-based immigration system, being introduced this year to ensure only those with skills the country needs are allowed in.
They will apply to "skilled" workers from this autumn and follow new rules already announced to apply to "highly skilled" migrants. Those for students will follow later.
Firms must show they cannot find British workers to do the job and would-be immigrants will have to show the work is skilled, they speak good English and earn over £24,000 or are well qualified.
Home Office analysis suggested 12% of non-European migrants who arrived last year under the existing work permit scheme would have been refused - around 8,000 individuals.
Even more would have been kept out under tougher rules applied to groups such as sportspeople, performers and charity workers wanting to come to the UK on a temporary basis.
They will not apply however, to those coming for one-off events such as the Edinburgh Festival or to compete in the 2012 Olympic Games in London.
Immigration minister Liam Byrne said: "Our new points system means that British jobseekers get the first crack of the whip and that only the skilled migrants we actually need will be able to come.
"By moving points up or down, we can make sure the numbers we allow into the UK are in line with the needs of business and the country as a whole.
"When we set the points pass mark, we will listen to independent advice - the Migration Advisory Committee (MAC) on the needs of the economy, and the Migration Impacts Forum (MIF) on the effect of migration on society."
The Home Office also claimed success in a clampdown on illegal working.
Mr Byrne said: "In 2007 we carried out 40% more illegal working operations than the previous year - and frontline officers have new powers to levy on-the-spot fines.
"These fines make up just one part of the biggest shake-up of the immigration system for a generation.
"With the introduction of compulsory identity cards for foreign nationals later in the year, there can be no excuse for not checking the identity of those applying for jobs."
Mr Byrne said employers would be forced, for the first time, to advertise positions in job centres before turning to overseas recruitment.
And he said a doubling of investment in skills should help ensure there were suitably-qualified British staff to fill the vacancies.