Opus International Consultants says lower council spending and the impact of Mainzeal's collapse led to a fall of 12.5% in its first-half net profit.
Net profit for the engineering company for six months ended June fell to $9.4 million compared with $10.8 million in the same six months last year.
Chief executive David Prentice said Mainzeal's collapse cost Opus about $500,000.
"It's been a challenging first half, particularly in New Zealand," he said. "But what we've found is a substantial pickup in the second quarter of that first half."
