Environment Minister Mark H Durkan's decision to approve a major mixed-used development on the outskirts of Newry was legally flawed, the High Court heard today.
Counsel for a body of traders in the city claimed the green-light was given for the multi-million pound Carnbane Way scheme despite failures in assessing the environmental impact.
A judge was also told the full extent of the proposals were not advertised - with allegedly no reference to a new bridge being built over the Newry River.
William Orbinson QC said: "We submit that the respondent made several errors of law in granting permission."
The Newry Chamber of Commerce and Trade is seeking to have the decision declared unlawful and quashed.
Developers The Hill Partnership are proposing to build 70 industrial and business units, a supermarket, 14 homes, a coffee shop, car parking and general landscaping on land straddling the river.
They have argued that the Department of the Environment wrongly concluded the development would not damage city centre investment.
When he granted planning permission last year Mr Durkan said he was satisfied the existing city centre retail offering was strong enough to compete with the new supermarket.
He added that the development should bring jobs and provide an economic boost for the area.
But according to the Chamber of Commerce the Department acted irrationally in the weight it gave to any economic benefits.
Further grounds of challenge include an alleged failure to comply with the Habitats Regulations in considering the potential effects of any pollution of Newry River and Canal.
Mr Orbinson also claimed a further flaw in not properly meeting Environmental Impact Assessment regulations.
Opening the application for a judicial review, he set out how the proposed development includes a new bridge over the river.
"The bridge looms large in this case both from an ecological and planning permission aspect," he said.
"It's not referred to in any description of the development and was not advertised."
Another attack on the ministerial decision centred on an alleged failure to refer the matter to the Stormont Executive.
According to Mr Orbinson it should have gone before the power-sharing administration as a "significant or controversial matter".
The case continues.