Up to 35 percent of a nation-wide bus company's drivers were employed on work visas last year, Immigration New Zealand says.
Immigration New Zealand (INZ) has been monitoring the number of migrant drivers employed by Go Bus and whether the company is following correct immigration procedures.
INZ spokesperson Darren Calder said up to 35 percent of the company's drivers were employed on work visas last year, and the ministry reviewed Go Bus' procedures last December.
He said Go Bus was advised to apply for permission to bring in significant numbers of migrant drivers in future.
The bus company, which is jointly owned by Ngāi Tahu and Tainui holdings, operates in Christchurch and Dunedin as well as several smaller towns.
Go Bus South Island operations director Nigel Piper disputed Immigration New Zealand's figures.
He said the company's figures showed only about 4.5 percent of its more than 2040 employees throughout the country were on work visas, which would be about 90 people.
It had not made any immigration applications since February 2015, it said.
Immigration New Zealand later said it knew of 88 Go Bus workers currently employed on work visas nation-wide.