The DUP has taken out a wraparound advertisement in a British free newspaper to convey the message that the party wants the UK to leave Europe.
The United Kingdom will vote on whether to remain in the European Union on Thursday 23 June.
Ahead of that vote, a four-page ad in the Metro newspaper urged DUP followers to vote to leave under the headline: "Take Back Control".
The paper is read by thousands of commuters in London and other cities.
But it is not available in Northern Ireland.
In the ad, the party lists a series of arguments against remaining in the EU. They also pointed to why they believe getting out is a "better" option.
Mervyn Storey, DUP, defended his party's decision to advertise in Britain.
"We are a national party, we are the fourth largest party in the House of Commons and, clearly, this is a national campaign," he said.
"Northern Ireland has not been on the periphery of this campaign, we in the DUP have been a central player in the Leave campaign and, therefore, it is as conceivable to take that ad in that publication as it is to take it in Northern Ireland."
Asked about the cost of the advertisement, he called it "a price worth paying" to get the party's message out.