Theresa May will visit Northern Ireland to give a speech on Brexit policy and meet business leaders on Tuesday.
The prime minister is expected to underline the UK’s commitment to ensuring there will be no hard border.
Her visit comes as the prime minister is due to try and reopen negotiations with the EU on the withdrawal deal and backstop.
Labour MP Keir Starmer, speaking in Belfast on Monday, said a backstop was an inevitable part of a Brexit deal.
The backstop is an insurance policy, designed to avoid a hard border “under all circumstances” between Northern Ireland and the Irish Republic.
It was part of the original withdrawal deal, agreed between the UK government and the EU.
However, with the withdrawal deal having been rejected in parliament over particular objections to the backstop, Mrs May will now try and renegotiate the deal with the EU.
Downing Street has said alternatives to the backstop are being explored “seriously” and with “urgency”.
The Dutch foreign minister said on Monday that it was “not reasonable” to expect there will be a completely different outcome to what has already been negotiated.
Previously, Mrs May had encouraged Northern Ireland businesses and farmers to get behind the backstop she had negotiated with the EU in order to avoid disruption to cross-border trade after Brexit.
In her speech in Northern Ireland on Tuesday, she must explain how her u-turn on the backstop squares with her commitment to avoid a hard border.
Sir Keir, his party’s Brexit spokesperson, said he had real concerns about the current backstop but that some version of it remains necessary.
He said he believes a combination of the UK being part of a customs union with the EU and aligning with the regulations of its single market can secure the UK economy.
He added it would ensure there was no hard border on the island of Ireland.
Sir Keir wants the prime minister to hold another Commons vote on the customs union proposal.
‘Not reasonable’ to expect different deal outcome
by John Campbell, BBC News NI economics editor
The Dutch foreign minister has said the EU is willing to listen to “specific proposals” on the Brexit backstop but so far none have been made by the UK.
Stefan Blok was speaking on a visit to the Irish border on Monday.
He said it was “not reasonable” to expect there will be a completely different outcome to what has already been negotiated.
He was joined on the border by Ireland’s Europe Minister Helen McEntee.
She said the backstop was needed to protect peace and the all-island economy.
She called on the UK government to live up to its commitments.
A group of MPs, including Brexit Secretary Stephen Barclay, and government officials are discussing alternative arrangements to the Irish backstop.
The Alternative Arrangements Working Group, consisting of Leave and Remain MPs, is holding three days of talks from Monday.
Meanwhile, Taoiseach (Irish prime minister) Leo Varadkar said the UK was reviewing ideas that had “already been rejected”.
Sir Keir said it was unlikely this approach would work at this late stage in the Brexit negotiations.
He added that the prime minister’s change in policy had raised anxiety levels in Northern Ireland.
What is the backstop?
The backstop is an insurance policy to ensure no hard border on the island of Ireland and would kick in if, two years after the Brexit, the UK and the EU cannot reach a trade agreement that avoided the need for physical border checks.
It would keep the UK in the “single customs territory” with the EU and leave Northern Ireland effectively in the EU’s single market for goods.
Critics fear the UK could be “trapped” in this arrangement for years, while Unionist MPs in Northern Ireland also fear it would divide Northern Ireland from the rest of the UK.
Parliament rejected the original withdrawal agreement over objections to the backstop.
Mrs May will now return to the EU and try to renegotiate the deal. However, the EU has said it will not reopen talks on the backstop.