Parts of the UK could be "swamped" by EU migrants unless rules change, the defence secretary has claimed.
Michael Fallon said it was vital to impose some restrictions on the free movement of people in the EU, as many towns feel "under siege" by workers and those claiming benefits.
His language attracted criticism, with Labour saying it was "desperate".
A Downing Street source later said Mr Fallon "accepts he should have chosen his words better".
He should have used the words "under pressure" instead, the source added.
Official figures published in August showed UK net migration - the difference between those entering and leaving - increased by more than 38% to 243,000 in 2013-14. EU citizens accounted for two-thirds of the growth.
It has been reported the UK could seek to apply an "emergency brake" to stop EU migration after it reached a certain level or to limit the number of National Insurance numbers issued to new arrivals.
But German Chancellor Angela Merkel said it would be wrong to "tamper" with the system in place across the EU.
'Vast movements of people'
Mr Cameron has said the relationship with the EU will be reformed ahead of an in/out referendum, to be held by the end of 2017, if his Conservative Party gains a majority at next year's general election.
Mrs Merkel appeared to reject the prospect of substantial change regarding immigration, telling the Sunday Times: "Germany will not tamper with the fundamental principles of free movement in the EU."
But Mr Fallon told Sky News: "The Germans haven't seen our proposal yet, and we haven't seen our proposal yet.
"That is still being worked on at the moment to see what we can do to prevent whole towns and communities being swamped by huge numbers of migrant workers.
"In some areas, particularly on the east coast, towns do feel under siege from large numbers of migrant workers and people claiming benefits. It is quite right that we look at that."
Mr Fallon added: "The original (European) treaty when it was drawn up 50 years ago did not envisage these vast movements of people, and we are perfectly entitled to say this needs to be looked at again.
"We will put our proposal forward and we will look for support from other member states as well, including Germany."
He said the Conservatives wanted "some control" on the number of people in the EU coming to the UK.
Mr Fallon added: "Things have changed in Europe. We have seen large movements of not just migrant workers but migrant benefit claimants as well right across Europe, and we are fully entitled to say this is making a difference to us that now needs to be dealt with."
Liberal Democrat Energy Secretary Ed Davey struck a different tone, saying: "There are more than a million British people living in Spain. There are hundreds of thousands of British people living in France.
"In fact there are tens of thousands of people living in almost every EU country and if we were to pull up the drawbridge on the English Channel, the truth is British people wouldn't be able to come and go because they'd take action against us."
The Conservatives face a strong challenge from the UK Independence Party (UKIP) - which advocates withdrawal from the EU - in next month's by-election in Rochester and Strood in Kent.
The contest was prompted by the defection of Tory MP Mark Reckless to UKIP.
For Labour, shadow foreign secretary Douglas Alexander accused Mr Fallon of "desperation" in his language.
He added: "We have got a government that is spending more time negotiating with its backbenchers than negotiating with other European leaders.
"The truth is, if you are looking out the back window of your car all the time, you tend to crash the car and right now David Cameron is so fearful of internal challenge on the issue of immigration and external challenge electorally from UKIP that I think he is letting Britain down."
Earlier this week Mr Cameron said he would not pay an extra £1.7bn demanded by the EU from the UK by 1 December. The organisation cited improvement to the economy as the reason for the hike.
Mr Fallon branded the figure "outrageous", adding: "Whether it is right that you should be taxed for the growth that you have had, and those countries that have not had successful growth policies should actually benefit - that does not seem right."