Finance Minister Sammy Wilson has rejected Assembly claims he is "not fit" to lead negotiations on lowering corporation tax which could cost Northern Ireland a £300m loss in its block grant.
SDLP leader Margaret Ritchie voiced concern that the DUP Minister is closer to North Down MP Lady Sylvia Hermon, who opposes the move, than his party colleague Enterprise chief Arlene Foster, an ardent champion.
Their clash came as MLAs from the five main parties - also including Sinn Fein, Ulster Unionists, the SDLP - united to support "in principle" the devolution of corporation tax powers to Stormont.
The show of solidarity landed ahead of this Friday's final deadline for the Treasury's consultation on the issue, coinciding with the start of the Assembly's nine-week summer recess.
Ms Ritchie said Mr Wilson's scepticism demonstrated the "laziness and lack of imagination" of his department and was closer to the outright opposition of Lady Hermon than to the unequivocally in-favour position of Enterprise Minister Foster.
"And he is completely at odds with the position of his colleague and party leader, the First Minister (Peter Robinson), who not only supports the lowering of corporation tax but argues that it should go below 12.5% to 10%," she added.
Asking whether Mr Wilson should be heading the detailed negotiations with the Treasury, she characterised his position as "excessive caution and fear of change masquerading as prudent management".
DUP figures, however, rallied to Mr Wilson's defence. Chairman Lord Morrow said Mr Wilson's caution was a "sign of maturity rather than weakness" and MLA Alistair Ross said the minister was right to inject some realism.
Mr Morrow also made clear, however, he did not share the total enthusiasm of others.
Warning that he suspected the block grant loss could be around £300m, he said: "There is no such thing as a free lunch and we will learn that very shortly."
But Mr Wilson insisted he did not differ from other ministers at all.
"Ms Ritchie said that I was not fit to lead the negotiations (but) different ministers have differing responsibilities: some are interested in job creation; others look at the wider benefits to society.
"As Finance Minister, my responsibility is to look also at the impact on public finances," he said.
All the main political parties as well as the business community have championed reducing the rate of corporation tax from the current 26% to something closer to the 12.5% in the Republic of Ireland, amid claims that it would generate 4,500 new jobs a year. After the last General Election the proposal was identified as an option in a Treasury paper on kick-starting the region's economy.