An investigation has been launched into companies contracted by lines company Chorus that allegedly used unpaid 'volunteers' or workers paid well below the minimum wage.
The Ministry of Business, Innovation and Employment (MBIE) confirmed that the Labour Inspectorate was investigating the employment practices of some contractors and subcontractors of Chorus.
A Chorus spokesman said the company had always been "very clear that the use of volunteers was completely unacceptable".
"As soon as we were made aware that a few people were taking part in the initiative we put an immediate stop to it," he said.
Chorus had always said it would co-operate with any investigation and should it show anything it would be dealt with swiftly.