(Bloomberg) -- Ireland is planning emergency legislation that would allow it to deport asylum-seekers arriving from Northern Ireland back to the UK, the latest salvo in a mounting dispute between the two countries over migration.

The proposed law approved by cabinet on Tuesday would override an Irish court ruling blocking the government from sending asylum-seekers back to the UK, on the grounds Britain’s new plan to deport migrants to Rwanda made it an unsafe destination under European Union law.

Tensions between Ireland and the UK have risen since new Irish premier Simon Harris’s administration appeared to blame Britain’s Rwanda plan for an uptick in the number of migrants crossing into the Republic from Northern Ireland.

Though the numbers involved are unclear, the row has the potential to escalate because it touches on a febrile political mood on both sides — as well as the years of tough Brexit negotiations following Britain’s decision to leave the EU.

Both governments have played down the tensions, saying they’re collaborating on a migrant influx affecting countries across Europe. Yet what ministers say to their domestic audiences underscores how their interests don’t align.

On Monday, as reports of Ireland’s proposed law began to circulate, Prime Minister Rishi Sunak quickly moved to rule out any deal with Ireland to accept returned asylum-seekers. He and other ministers also appear to have embraced the Irish view that the Rwanda deportation plan is driving migrants into Ireland, arguing that it shows the policy is having the desired deterrence effect.

Sunak’s spokesman, Dave Pares, also said the government sees the issue as part of a broader question about UK ties to the EU. There can be no deal with Ireland, he said, without a reciprocal agreement that lets Britain send people arriving on small boats across the English Channel back to France.

Stopping those boats is one of Sunak’s main promises to voters as he tries to keep his Conservatives in power after 14 years. The Rwanda plan is central to that, and Sunak has talked up its efficacy ahead of local elections on Thursday.

But to his critics, Sunak’s Rwanda plan and his response to Ireland illustrate a fundamental flaw, that his government is acting out of political self-interest that appears to rule out cooperation with other nations. Sunak’s critics on the Tory right, for example, would likely try to oust Sunak if he cut a deal with the EU that left the UK accepting any migrant quotas, for example.

Yet provoking Ireland does carry risk for Sunak, given the British premier regards solving the questions around how Northern Ireland would operate after Brexit, and soothing UK relations with the EU as his major achievements.

If migrants asylum-seekers are arriving in the Republic from Northern Ireland — Justice Minister Helen McEntee put the number at 80% of recent applicants — that will heap scrutiny on one of the central tenets of the Brexit deal with the EU, that the border on the island of Ireland should be all but invisible.

There’s also a core difference between the UK’s relationship with France and its link to Ireland — the Common Travel Area. That underpins a post-Brexit agreement between the two countries in 2020 on asylum-seekers, which Ireland’s proposed legislation would re-assert. 

“We have a legitimate expectation that agreements between two countries are honored,” Harris said on his way into the cabinet meeting Tuesday. 

Immigration has emerged as a key theme in Irish politics ahead of a national election due next year and local votes in June. There have been protests at accommodation earmarked to house asylum seekers, highlighting tensions in local communities about a lack of resources. More than 1,700 asylum-seekers are currently without accommodation.

The spat with the UK appears to have some way to run. Asked about Ireland’s plan to send police officers to the border area, Sunak’s spokesman appeared to indicate the UK regards that as a violation of the Common Travel Area.

Yet taking a tough line is still a political gamble. Effectively, Sunak’s government is arguing that it has no responsibility to stop asylum-seekers leaving the UK across an open border into the Republic, even as it accuses France of not doing enough to stop migrants leaving its shores for Britain.

It’s an argument that makes political sense in Sunak’s Conservative Party, but one that will rile officials in Dublin and likely Brussels, too.

--With assistance from Alex Wickham.

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