The Employment Relations Authority will decide by Tuesday whether Air Nelson has been using illegal strike-breakers while the airline's own employees take industrial action.
The Engineering, Printing and Manufacturing Union claimed managers from the airline's parent company Air New Zealand were doing the work of the strikers.
The
union's aviation spokesman Strachan Crang said the authority would issue its ruling by Tuesday.
On Monday Air Nelson general manager John Hambleton said the company's legal adviser viewed the allegations last week, adding: "We're confident that Air Nelson has complied with the law at all times."
He said the four workers in question were completing work for Air New Zealand, not Air Nelson.
"We're kind of surprised the EPMU is taking this action because it was explained by letter on Friday as to what the situation was."
The airline's staff are seeking a two-year contract with increases of 5.8 per cent and 4.8 per cent, which included catch-up payments to compensate for earlier low pay settlements. Because no agreement had yet been reached, the staff were staging rolling strikes for four days every fortnight.
Air Nelson's engineers and flight operations crew were also refusing to load fish and food on to the planes, de-icing the planes in the mornings or to work overtime, Mr Crang said.
It is not known whether the parties will meet before the next scheduled strike on June 6.
- NZPA
