The Democratic Unionist Party has been quick to make clear its grievances with British Prime Minister Boris Johnson's Brexit deal.
Negotiators worked well into the night in Brussels and are understood to have felt a major breakthrough had occurred, making an exit agreement at the European Council look likely.
But the DUP put out a statement laying out their concerns with the draft terms.
Here is a look at what the party's main concerns are on each of the three issues:
The European Union and Mr Johnson moved towards each other on a customs arrangement for Northern Ireland.
Mr Johnson is reported to have ditched his "two borders" proposals and will instead accept the six counties will remain in a customs union with the Brussels in all but name.
The EU, meanwhile, has agreed for Northern Ireland - in what would be a complex dual-tariff arrangement - to be allowed to officially remain in a customs territory with the UK, meaning the region can benefit from trade deals inked by the Government and any lower tariffs agreed by ministers.
The arrangement would keep the Irish internal border open but create checks in the Irish Sea on goods travelling between Northern Ireland and Great Britain, a situation that crosses the DUP's "blood red" line.
Ms Foster had previously said: "There cannot be a border down the Irish Sea, a differential between Northern Ireland and the rest of the UK. The red line is blood red."
Conservative leader Mr Johnson often labelled his predecessor Theresa May's backstop plans "undemocratic" and sought a mechanism to give Northern Ireland an opt-in or way out of his Withdrawal Agreement.
The EU rejected plans to give the Stormont Assembly a veto every four years on the border deal but is said to have conceded to a unilateral exit arrangement, using a vote mechanism concocted by Assembly members.
A rejection of the plans by the Assembly, which is currently suspended, would bring in a two-year cooling-off period in which a way of saving the Good Friday agreement would need to be found, according to The Times newspaper.
The DUP fears that moves to bypass the petition of concern - a unique political tool that allows unionist or nationalist groups to reject reforms in Northern Ireland - could upset the balance of the once-warring communities.
Brussels and the UK are reportedly in a wrangle over VAT and whether EU rates should apply in Northern Ireland.
The objection from Downing Street was described by EU diplomats as a "British smokescreen" to give Number 10 more time to win over the DUP, according to The Guardian.
How concerned Ms Foster is about staying with the UK's VAT rate is unclear, and whether she is using the disagreement to show there are issues being voiced by more than just her own party remains to be seen.