The Public Service Association in Tonga says it is considering legal action to stop a new salary structure coming into force this month.
The overhaul came after a nearly two year review by the Remuneration Authority which sought to modify job descriptions to better fit what people did and link pay with performance effectively.
But the PSA General Secretary Mele 'Amanaki says the structure was unfair and the review lacked transparency, with not enough consultation carried out.
The PSA presented a petition to Cabinet to delay the new structure implementation until next year.
Ms 'Amanaki said if it was ignored, PSA members would not strike as the last major strike in 2005 damaged the economy, but there were other options.
"What we have promised the people that we will try and negotiate through consultation using the law," she said.
"If Cabinet doesn't approve it then we can make a petition to the King and the Parliament, that's provided for us (through the Constitution), or we can apply for an injunction through the Supreme Court to have government stop everything and have a judicial review carried out."