The Fiji United Freedom Party alleges that members of the military have harassed and attempted to intimidate its officials.
The party's co-leader, Nayagodamu Korovou, says two vehicles full of men approached the party's treasurer and vice-president and threatened to take them away.
Mr Korovou says the men also swore and verbally abused their members.
"We know they're military because we know the people who came in civilian clothes. They were looking for our treasurer and trying to ask him some questions about, blaming us about plotting something to kill the Prime Minister."
Mr Korovou says he hasn't gone to the police with his allegations because he has no faith in their work and believes they are biased.
A senior officer in the Republic of Fiji Military Forces, Lieutenant-Colonel Sitiveni Qiliho, says he will look into the allegations, but says he doubts the men were military acting under any orders.
"It's not the RFMF's job to do such things. We've had elections. We have a democratically-elected government in place and the RFMF is supportive of the government that has been elected and we are here to play our role in support of government. That doesn't mean taking part in such allegations. That's not part of a democratic process."
Lieutenant-Colonel Qiliho says he can't just ignore the allegations but he has suggested they also be taken to the police for further investigation.