The DUP says as things stand, it cannot support a Brexit deal currently on the table between the EU and UK.
The party says it has issues with the customs and consent mechanisms in the draft deal.
It also feels there is still a lack of clarity around VAT.
It comes as Brexit negotiations went on overnight in an attempt to reach a last-minute deal.
The two sides are said to be close, but the issues around how VAT will work in Northern Ireland remains.
Without the DUP, it will be difficult for the British Prime Minister Boris Johnson to get any agreement passed in the UK House of Commons.
DUP leader Arlene Foster and deputy leader Nigel Dodds released a joint statement this morning.
"As things stand, we could not support what is being suggested on customs and consent issues and there is a lack of clarity on VAT."
"We will continue to work with the Government to try and get a sensible deal that works for Northern Ireland and protects the economic and constitutional integrity of the United Kingdom", they said.