?Sinn Féin leaders are due to hold Brexit talks with Jeremy Corbyn later on a day of meetings in London.
Party president Mary Lou McDonald and vice-president Michelle O'Neill are also set for discussions with Secretary of State Karen Bradley.
They will also meet a number of SNP MPs at Westminster.
On Sunday, Mrs McDonald said she would tell the Labour leader that Irish interests must be protected whatever the outcome of his Brexit negotiations with British prime minister Theresa May.
Mr Corbyn is due to meet the republican leaders late this afternoon.
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"We will set out again the very clear need to protect Irish interests and make it very, very clear that whatever way Brexit lands, deal or no deal, that Irish interests have to be protected," said Mrs McDonald.
"Our peace process, our all-Ireland economy, crucially our citizens' rights, cannot be the collateral damage to the Tory Brexit."
At the weekend, Mrs McDonald also confirmed that Sinn Féin will hold a convention this weekend to select a candidate to fight a potential European election in Northern Ireland.
"If an election happens, we will fight the election," she said.
"We are ready."
Sinn Féin leader Mary Lou McDonald said Brexit uncertainty is causing "real harm" on the island of Ireland and a customs union would not fully solve the border issue.
Speaking ahead of talks with Labour's leader, Ms McDonald told the Today programme: "I hope to get some sense from Jeremy Corbyn as to where he thinks all of this might land.
"There is a lot of talk now about an extension... and there's ongoing uncertainty which I'm sure has caused real problems in Britain and certainly has caused real harm on the island of Ireland."
Praising Mr Corbyn as someone who "understands Irish politics very deeply" unlike "in Government circles", Ms McDonald said a customs union would only solve the issues around the Northern Irish border "to an extent".
She said: "It (a customs union) doesn't answer in its entirety the issue for the all-Ireland economy.
"Yes it is about the customs union but it's also about alignment to the single market."
Michel Barnier will hold talks with Leo Varadkar in Dublin later ahead of this week's crunch summit in Brussels.
The EU's chief Brexit negotiator will discuss the latest developments with the taoiseach this afternoon.
Looking forward to welcoming @MichelBarnier and team to Dublin again today. As ever, we will be working together to achieve a fair and orderly #Brexit - protecting EU and Irish interests while respecting UK. Important week ahead! #StrongerTogether
— Simon Coveney (@simoncoveney) April 8, 2019
Mr Barnier will also meet Tánaiste and Foreign Affairs Minister Simon Coveney and Finance Minister Paschal Donohue.
The engagements at Government Buildings in the city come prior to the meeting of the EU27 on Wednesday when European leaders will discuss Theresa May's request for a further Brexit extension.
At the weekend, Mr Varadkar said his own preference was for a longer extension than the June 30 date proposed by the UK.
"What we want to avoid is an extension that just allows for more indecision and more uncertainty," he added.
Mr Varadkar also said the prospect of one of the EU27 saying no to any form of extension at the European Council meeting was "extremely unlikely".
The Taoiseach said any country that vetoed a further Brexit extension would not be forgiven by other member states.
Mr Barnier's visit is the latest evidence of intensifying diplomatic exchanges between the Dublin government and key EU figures in the Brexit process.
Last week, Mr Varadkar held bilateral meetings with French president Emmanuel Macron in Paris and German chancellor Angela Merkel in Dublin.
