The poster, circulated by the pro-Brexit, anti-immigration UKIP party, shows a huge line of migrants snaking into the distance, with the words "Breaking Point" written over them.
The unveiling of the poster comes as Europeans living and working in the United Kingdom ponder what an exit might mean for their freedom of movement across the EU.
Both sides in the referendum debate are preparing to make a final push before the Thursday vote after a three-day break.
Polls show the electorate is evenly split between the "Leave" and "Remain" camps.
British Prime Minister David Cameron describes leaving the EU as a 'leap in the dark' and is making the case for remaining in the EU.
"It stands to common sense that we will have less growth, we'll have less jobs, we'll have less livelihoods for people in our country. So if that happens, you don't gain money by leaving the EU, you actually make your economy smaller, you have fewer jobs, you have less tax revenues, so therefore you have a big hole in your public finances."
Immigration and the economy have defined the debate and following the murder of MP Jo Cox, allegedly by an anti-immigration supporter, questions have been raised about the tone of the campaign from both sides.
Criticism has been levelled at the anti-immigration U-K Independence Party, or UKIP, which is advocating Britain's withdrawal from the European Union.
The party has unveiled a poster showing a huge line of migrants snaking into the distance, with the words "Breaking Point" written over them.
UKIP says it will replace the controversial billboard, but leader Nigel Farage adds that his party's view on immigration is about taking back control of the country's borders.
"When you challenge the establishment in this country, they come after you, they call you all sorts of things. And to be honest, all we have said in this referendum campaign is we want to take back control of our lives, take back control of our borders and put in place a responsible immigration policy."
Britain's Labor Party and the Cameron government have both condemned the poster.
British Chancellor George Osborne described is as disgusting and vile with echoes of literature used in the 1930s.
He says there are better ways of debating immigration policy especially in light of the murder of MP Jo Cox.
"Because of the tragic death of Jo we can have a less divisive political debate in our country. There are perfectly legitimate concerns about migration. Concerns that are felt in every western democracy in the world but I think there is a difference between expressing these concerns in a reasonable way and whipping up concerns, whipping up division."
There are currently 65 million people in the United Kingdom with three million holding an EU passport: that's about five per cent of the population.
Beyond the impact on refugees and migrants seeking asylum in Europe, the possible effects of the UK leaving the EU could also be felt by migrant workers already in the UK and British workers abroad.
At this stage there's no suggestion Europeans would be forced out in the event of a Brexit, but if they were subjected to the same salary criteria as non-EU migrants, 80 per cent of them would fail to qualify.
Dr Sebastian Kalwij is a Dutch migrant who has lived in the UK for 20 years.
"I think the atmosphere has changed. People have become far more anti-European. The reality is it makes life less pleasant; it makes you wonder why do you stay in a country, which is so anti-European? I might as well move to a country where they appreciate fellow Europeans."
And what about the 1.2 million UK citizens living in Europe?
These expat workers are concerned.
"We may be classed as aliens."
"I think a lot of people will leave here and go back to England. And they'll just have to find places to put us in England."
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