As reported by Reuters, Northern Ireland's DUP party aimed a shot across the bow of UK Prime Minister Theresa May, withholding their votes on key issues as a display of discontent with the PM's latest Brexit agreement with the EU.
Pedro Sanchez said: "As of today, if there are no changes with respect to Gibraltar, Spain will vote no to the agreement on Brexit".
Spain maintains a claim to Gibraltar after it was ceded to the British crown under the 1713 Treaty Of Utrecht, and through the Brexit negotiations Spain has conducted separate talks with the United Kingdom government over the future of the border.
The withdrawal agreement sets out plans for a 21-month transition after Brexit, in which Britain and the European Union want to turn their outline agreement on the future relationship into a full trade deal.
On Wednesday the leadership of the all-Ireland trade union movement at its executive meeting in Belfast considered its response to the draft agreement negotiated between the EU and UK. Madrid is concerned that Article 184 would in effect extend any deal on the future agreement to Gibraltar without Spain first having a say.
"It's no surprise that we are seeing the Spanish government raise issues at the last minute", complained Gibraltar's chief minister Fabian Picardo.
The Spanish flag flies at the Gibraltar-Spain border, in front of the Rock in the British overseas territory of Gibraltar, historically claimed by Spain, in La Linea de la Concepcion, southern Spain, November 15, 2018.
Critics of the agreement struck by May believe it gives away too much to the EU, including control over locking the United Kingdom into a Customs Union in future.
"The future negotiations over Gibraltar are separate", Borrell told reporters in Brussels.
Spain's foreign minister, Josep Borrell, told Politico today that it was the fault of EU negotiators, who neglected to include text already agreed between the United Kingdom and Spain despite multiple previous confirmations with European officials.
May faces pressure from her Northern Irish allies, who oppose a deal they say weakens British sovereignty in their province, and from Spain, which warned it might oppose the accord over Gibraltar.
"We no longer have a functioning government".
"As a country, we can not accept that whatever happens with Gibraltar in the future will depend on a negotiation between the United Kingdom and the European Union".
"If the Government can't negotiate an alternative then it should make way for those who can and will", he said. We have given direction to our negotiators this evening.
The tension between the parties has arisen due to the DUP's rejection of the so-called Brexit backstop in Mrs May's European Union withdrawal agreement.
After Tuesday's meetings in Madrid, the Gibraltar Government said the memorandums and the tax agreement were now complete "subject only to text stabilisation, legal checks and minor clarifications".