Fifteen people, including members of the Fiji Labour Party, are being questioned at a police station in Lautoka on Thursday.
FBC News reports that police have confirmed making the arrests on Wednesday night.
Fiji Labour Party leader Mahendra Chaudhry says he has been told the 15 are awaiting a police decision on whether they should be charged with holding a meeting without a permit.
Mr Chaudhry says the group was having a yaqona session (a ceremonial drink) at a private residence when police barged in.
"The Labour Party had not scheduled any meeting in the area. So this is just plain intimidation and harassment of Labour Party activists and supporters as I can see."
Mr Chaudhry says he questions how Fiji can move towards a new constitution if police behave this way.