The number of migrants allowed into the UK under the points system may have to be reduced because of the economic crisis, an immigration minister says.
Phil Woolas told the Times immigration became an "extremely thorny" subject if people were losing their jobs.
"It's been too easy to get into this country in the past and it's going to get harder," he said.
The Home Office said the new points-based system provided "a powerful and flexible set of controls".
The government recently introduced a points-based system to attract migrants from outside the EU judged to be most valuable to the economy.
| There has to be a balance
between the number of people coming in and the number of people leaving
Phil Woolas Immigration Minister
But Mr Woolas, who became immigration minister in the reshuffle earlier this month, said: "This government isn't going to allow the population to go up to 70 million.
"There has to be a balance between the number of people coming in and the number of people leaving."
Figures from the Office for National Statistics show the population grew by nearly two million to almost 61m people between 2001 and 2007.
Various official projections predict this to rise to 77m in 2051 or 110m in 2081.
Keith Best, of the Immigration Advisory Service, said migrants tended to get blamed
BBC political correspondent Ross Hawkins said it was significant Mr Woolas had quoted 70 million as an upper limit for the UK population.
The government had, before now, fought shy of setting a "population policy" because it was difficult for ministers to explain how it would be managed, he said.
This is because immigration from inside the EU cannot be controlled, and neither can a limit be placed on genuine claims for asylum.
Our correspondent said this meant there would be "all sorts of questions raised" about how the government was going to achieve its aim.
Former Labour minister Frank Field, who is a member of a cross-party group on immigration, welcomed the government's seeming change of emphasis.
| The Conservatives want to know
what the government will do to put its new population policy into
The BBC's Ross Hawkins
But he said: "When we're moving into a recession, the length of which we do not yet know, the immigration policy suitable for a boom is totally unsuitable for a recession."
He said the key was to "break the link" between people coming to the UK to work and gaining citizenship, which increased the population.
Sir Andrew Green, chairman of Migrationwatch, which argues for balanced migration, told BBC Five Live Mr Woolas's remarks showed a significant development in the immigration debate.
"I think this could be a significant turning point. I think the economic crisis has shown up the weakness of uncontrolled immigration.
| The immigration policy suitable
for a boom is totally unsuitable for a recession
Frank Field MP
But the chairman of the Commons Home Affairs Select Committee, Keith Vaz, told the Times he would be "astonished" at a Labour immigration minister "in effect changing the policy".
The Labour MP added: "His predecessor and the home secretary have made it very clear they do not support a quota."
Keith Best, chief executive of the Immigration Advisory Service, told Today there was a danger Mr Woolas's comments could be misinterpreted.
| From what Phil Woolas is saying
this morning he appears to agree with us now
Shadow immigration minister Damian Green
An economic downturn would mean fewer people would be attracted to the UK for work anyway, he said - but some skills shortages would still exist even in recession.
Shadow immigration minister Damian Green said it appeared Labour was following Conservative policy.
"We've argued for an annual limit, the government has argued against it. From what Phil Woolas is saying this morning he appears to agree with us now - that's fine."
Chris Huhne, the Lib Dem's home affairs spokesman, argued the UK did not just need a population policy, but a regional policy as well.
"Some parts of the country still have declining or stable populations, while the South East is now reaching the limits of what can be sustained with its water resources," he said.
A Home Office spokesman said the points-based system allowed it to "raise or lower the bar" according to needs.
He added: "Our tough new Australian points system, plus our plans for newcomers to earn their citizenship, will reduce overall numbers of economic migrants coming to Britain, and the numbers awarded permanent settlement.
"Crucially, the points system means only the migrants with the skills Britain needs can come - and no more.
"Had the points-based system been in place last year, there would have been 12% fewer people coming in to work through the equivalent work permit route."