The number of skilled workers allowed into the UK from outside the EU is to be cut by 1,300, Home Secretary Theresa May has said.
Numbers will fall to 24,100 between now and April 2011, 5% less than last year.
Ministers says the temporary measure will cut the flow of immigrants while they hold a consultation on the right level for a permanent cap.
Labour's Alan Johnson said it was a pointless "gimmick" which didn't affect migration from the EU or students.
The cap will only apply to highly skilled migrants and skilled workers in certain categories of job. It does not apply to workers from EU countries, who are free to take jobs in the UK and make up a third of all foreign-born workers in the country.
But the coalition government argues it will help them achieve their objective of cutting net annual migration to the levels seen in the mid 1990s - a key Conservative election pledge which has survived the coalition agreement with the Liberal Democrats, who had previously opposed a cap as unworkable.
Mrs May told BBC Radio 4's Today programme there was "clear agreement" in the coalition government that a permanent cap would be set next April, but the temporary limit was needed to prevent a "rush of applications" before then.
"Immigration into the UK has been good for us but uncontrolled immigration is not, so we need to bring in these controls," she said.
Immigration had been a "key issue" during the election campaign and it was important to "deliver on promises made," she added.
Mrs May later said that the decision on where the annual cap should be set would take into account the social impact of immigration such as the pressure on schools, hospitals, council housing and other public services.
The Migration Advisory Committee will look at what the limit should be and report by the end of September.
Companies have been given 12 weeks to respond to suggest changes - including forcing employers to provide private health insurance for foreign workers in an effort to reduce any "undue burden" on the NHS.
Companies bringing in employees could also be told to show a commitment to training British workers.
Announcing the plans in the House of Commons, she said the government would introduce further immigration curbs, particularly on students, "in due course".
Ms May said the threshold for gaining entry as a highly-skilled migrant had been increased by five points to ensure only the "brightest and the best" non-EU migrants are admitted to the UK.
Business Secretary Vince Cable has reassured firms wanting to recruit from outside the EU that the cap will be implemented "in a flexible way" and could be introduced in a way that would not damage the economic recovery.
But it has been attacked by business groups, with the Federation of Small Businesses calling it the "economics of the sixth form".
Business fear the cap could stop them from filling vacancies at times of high demand, and other critics say it could have a detrimental effect on higher education, which is reliant on income from foreign students.
Mrs May announced the move in a written statement as she launched a consultation process for deciding the level of the permanent cap to be in place by next April. The government's Migration Advisory Committee, a group of independent experts, will study the economic and social impact of a cap and come up with its recommendation as part of the process.
Immigration minister Damian Green said it was important to "strike the right balance so that we can bring in the people that Britain needs but not at the rate we have had over the past decade that has given rise to so much tension".
The latest official immigration figures show that more than 500,000 people came to the UK in 2008. Almost half of those were returning British nationals or EU citizens.
Shadow home secretary Alan Johnson said a temporary cap was a con trick. He said it would affect about one in seven immigrants and there were already restrictions on firms recruiting workers from outside the EU under the points-based system introduced by the previous Labour government.
Mr Johnson told BBC News: "You wonder what is the point of this, given that in this country at the moment, under our policy, if a company wants to bring a skilled worker in, they can do it if they have advertised that job for four weeks in Job Centre Plus and they are absolutely sure they can't get a British worker to do it.
"So it's absolutely pointless. At best it's a gesture. At worst it's a deceit."