FILE PHOTO: Democratic Unionist Party (DUP) Deputy Leader Nigel Dodds speaks at the DUP annual party conference in Belfast, Northern Ireland November 24, 2018. REUTERS/Clodagh Kilcoyne

BELFAST (Reuters) - The Northern Irish party that props up Prime Minister Theresa May’s government said the European Union’s letter providing more reassurances over the introduction of backstop provision on Ireland’s post-Brexit border does not go far enough.

Parliament is due to vote on Tuesday on whether to back May’s withdrawal deal from the European Union after postponing the vote last month because the government was going to be defeated.

As part of the effort to get the deal approved by parliament, the EU is due to set out some assurances in a letter on Monday, EU officials said.

“The letter isn’t legally binding,” DUP deputy leader Nigel Dodds told BBC radio. “The prime minister will struggle to justify what the delay was about.”