A union leader is concerned a precedent could be set which would challenge New Zealand's sovereignty if the Government changes labour laws to entice Warner Brothers to film The Hobbit in the country.
A decision on where American studio Warner Bros will make the movies is expected by the end of the week.
A meeting last night between Warner executives and senior Government ministers pinpointed labour laws as the greatest issue.
Mr Key said the "paramount" problem was that film workers on independent contracts could be legally seen as employees, even if their contracts specifically called them contractors.
That followed a Supreme Court ruling in 2005 on James Bryson, a model maker on the Lord of the Rings movies, who was deemed an employee, even though he was hired as a contractor.
"They're not arguing people can't be employees," Mr Key said.
"They're just saying that if someone is engaged by their production company as a contractor, they want to know if that's how it's going to end up, and if it doesn't, that has other economic consequences for them.
"They're out of here, if we can't give them the clarity. There's no question about that."
But Council of Trade Unions President Helen Kelly this morning accused the Government of manipulating the situation to push through labour changes which could disadvantage workers.
"I think the Government is being very opportunistic - they've shown a disregard for workers rights (in the past)," she told nzherald.co.nz.
Ms Kelly said the move could set a precedent.
"If this is their response to this corporation - what about the next corporation and the next corporation?
"This Government is getting angsty about selling land to foreigners - well we can't sell laws to foreigners either. We are a sovereign nation.
Ms Kelly said the discussed changes were unrelated to the dispute, which she said was "completely settled".
The Media Entertainment and Arts Alliance and the associated New Zealand Actors' Equity have promised no further industrial action will be taken against the two films.
"Clearly a group of actors wanting a collective agreement is not the issue here," she said. "What they are worrying about is financial assurances."
Employment law specialist
Employment law specialist Jane Latimer said it was impossible to give that guarantee without changing the law.
"The current law cannot give them that assurance, because every person who works for any organisation is entitled to apply to the Employment Relations Authority or the court for a declaration as to their status employee or contractor.
Under current law, it did not matter what the contract said.
What mattered was "what the parties intended and what the true nature of the relationship is".
A new law would have to be introduced to ensure film workers hired as contractors would retain that as their legal status.
"It would almost have to be The Hobbit Amendment Act. It would have to be a special amendment to the law just for this case. Then that is a guarantee," Ms Latimer said.
Mr Key said all options were on the table, including looking at a special law for this project, or a special law for all film workers.