The threat of a trade war with Europe would not give the British government cause to overrule unionist objections to future EU trade laws in Northern Ireland, a senior U.K. minister has pledged.

Northern Ireland Secretary Chris Heaton-Harris made the commitment Tuesday to the Commons EU scrutiny committee, on the eve of a parliamentary vote to approve regulations governing the so-called Stormont Brake.

The “brake” is a key part of the Windsor Framework, the wider U.K.-EU agreement on making post-Brexit trade rules work in Northern Ireland. Northern Ireland remains the only part of the U.K. still bound to EU goods regulations.

The new laws published Monday offer unionists in the Northern Ireland Assembly the power to object to future EU laws governing goods standards — but also gives London ill-defined wiggle room to disregard such a unionist petition if U.K. ministers cite “exceptional circumstances.”

Democratic Unionist MP Gavin Robinson told Heaton-Harris the Stormont Brake was therefore not a genuine veto for Northern Ireland, and said the rules give London too much latitude to overrule unionist objections.

He raised the prospect of Brussels introducing retaliatory measures should Belfast seek to block new EU laws, and pressed Heaton-Harris on “whether you are satisfied that the threat of remedial action from the European Union would not constitute an exceptional circumstance.”

Heaton-Harris quickly shot back: “Yes.”

But when Robinson asked whether the senior U.K. officials flanking him agreed with that assessment, they demurred.

“I’m not seeking to provide definitional elements here as to what it means,” replied Mark Davies, director of the Windsor Framework Taskforce at the Cabinet Office. “If there are exceptional circumstances, ministers need to account for that to parliament.”

MPs are expected to vote through the new rules Wednesday, despite DUP opposition.