The union representing Australian pilots is launching legal action under new workplace laws claiming Qantas is underpaying New Zealand pilots to fly its trans-Tasman route.

The Australian and International Pilots Association (APIA) says 1,000 Qantas pilots are on leave and New Zealand-based pilots are flying the route for the Qantas offshoot Jetconnect.

The association is challenging the move in the Fair Work Australia tribunal.

New Zealand pilots are earning less than half of the minimum required under Australian terms and conditions.

These are Qantas aeroplanes with a Qantas logo flown by News Zealanders... and Australian pilots or Australian-based pilots are not happy

Qantas will not comment on how much the New Zealand pilots are paid

JetConnect is a New Zealand operation and pilots are therefore subject to New Zealand workplace laws.