The Home Affairs Department said on Thursday it had written to district councillors across the SAR, warning them against encouraging or helping people to take part in unauthorised assemblies.
The department said it acted after receiving complaints about councillors engaging in "activities which are unrelated to [council] duties, damaging to community harmony and possibly in breach of the laws of Hong Kong".
The warning came ahead of Friday's 32nd anniversary of the bloody crackdown on democracy protesters in Tiananmen Square, and follows a decision to ban the annual candlelight vigil in Victoria Park on health grounds for the second successive year.
The letter warns councillors that under their code of conduct, a member should not "place himself or herself in a position which may be contrary to the generally assumed standard of conduct expected" of a councillor.
They are also warned of the code's provision against councillors their allowances or office expenses for purposes unrelated to their role as a council member.
The department says that expenses used for activities that don't meet the code of conduct will not be reimbursed. It also warns of criminal liability if legislation is breached.
A large police presence is expected across the SAR after calls went out for gatherings at various venues. Most officers are expected to gather at Victoria Park, where the vigil usually takes place.