The DUP has said that if they do not like any deal that the British Prime Minister Boris Johnson may get with the EU, the party will vote it down in Westminster.
In an interview with RTÉ News, Ian Paisley Jnr warned Boris Johnson would need the party's ten votes and he said if Mr Johnson wants them, he needs to earn them.
"I think Boris Johnson would be very sensible not to try and cast the DUP under any bus or onto any railings. Boris Johnson.... needs our ten votes. If he wants them, like Theresa May, he’s got to earn them. If he doesn’t earn them he doesn’t get them".
Mr Paisley Jnr also refused to rule out a referendum in Northern Ireland as a mechanism for consent, but he said it was not what the party was proposing.
He said the DUP believed the assembly should have a say and he did not want to see that proposal watered down or beefed up.
He said the DUP maintains its position that it will not be leaving the EU separately from the UK or be "trapped" in a customs union.
He also said that any regulatory changes will require a "democratic veneer".
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Earlier, DUP leader Arlene Foster said any Brexit deal that traps Northern Ireland in EU structures will not get DUP support, Arlene Foster has warned.
The DUP leader said her party would only back a withdrawal agreement that is in Northern Ireland's "long-term economic and constitutional interests".
Ms Foster acknowledged there had been a lot of speculation as to what had happened during British Prime Minister Boris Johnson's meeting with Taoiseach Leo Varadkar in England yesterday.
The positive read out from Thursday's encounter, followed by the intensification of UK and EU negotiations, has prompted suggestions both sides could be poised to make compromises on customs arrangements, to avoid border checks on the island of Ireland.
Responding to the developments, Ms Foster said Boris Johnson was aware of the DUP view that the UK had to leave the EU as one nation.
She made clear her party would exercise its "considerable influence" in Parliament to stand up for the region.
"We are regularly in touch with the Prime Minister and as a result he is aware of our views," she said.
"The United Kingdom EU referendum result delivered the people's verdict and it must be delivered. To do otherwise would be anti-democratic.
Ms Foster said no barriers to trade could be erected within the UK.
She stressed the importance of Northern Ireland politicians giving democratic consent to any arrangement that might align the region with specific sectors of the single market.
"We have held steadfast to that position whilst recognising the need to be flexible and look at Northern Ireland specific solutions achieved with the support and consent of the representatives of the people of Northern Ireland," Ms Foster added.
