Fiji's opposition National Federation Party says if police keep harassing unions it will alert the United Nations.
The NFP leader Biman Prasad said police had interviewed public sector union executives and emails had been confiscated.
He said the police commissioner should reveal whether police acted on a complaint filed by Government or any other party.
And he said the attorney-general, the minister for civil service and the minister for defence should immediately ask the police commissioner to tell his officers not to get involved in the dispute.
Unions decided to hold a secret ballot to seek mandate for strike action following the government's move to put civil servants on contracted employment.
Dr Prasad said Fiji was not a police state, but he said such action did not augur well for Fiji's bid to become a member of the United Nations Human Rights Council.