Home Secretary Alan Johnson has announced plans to force employers to advertise jobs to British nationals for at least one month before they can be offered to migrant workers.
It is seen as a move to placate jobless construction workers.
Unemployed construction workers from the Unite and GMB unions gathered this week at Uskmouth, Newport, where a gas-fired power station is being built to protest over the use of foreign labour in the construction industry.
Johnson, accepting in full the recommendations of the Government’s immigration advisors, said he would double the legal minimum period from two to four weeks as of next year.
He also announced plans to increase the minimum wage for skilled workers by £3,000, to £20,000.
A scheme to increase the qualification period for workers transferring from other countries from six months to a year was also disclosed.
Experts estimate that one in 10 of the non-EU workers given permits last year would be excluded under the new rules.
Johnson said: “These changes will ensure that businesses can recruit the skilled foreign workers that the economy needs, but not at the expense of British workers, nor as a cheaper alternative to investing in the skills of the existing workforce.”