Police in Dunedin say about 200 people are travelling to the city from Christchurch as part of an unofficial Undie 500.
Extra police have been called in from around the lower South Island, in an attempt to quash any repeat of rioting during last year's Undie weekend.
Inspector Dave Campbell says the rally of mostly undecorated cars and vans is expected to arrive in Dunedin late on Friday.
He says in previous years, the students have come in dribs and drabs, but on Friday they were sticking together in a convoy.
The Otago Polytechnic Students' Association is threatening to expel any of its members found guilty of illegal activities during any Undie 500 related events.
The official event was cancelled after widespread rioting in Dunedin last year, but an unauthorised event is expected to take place.
The association's co-president Ryan Ward says the body won't tolerate appalling behaviour.
He says they will lose their ID card which entitles them to student discounts around the city and free access to the student gym, and they'll also be denied access to any clubs and societies.
Mr Ward says the mass disorder at last year's Undie 500 damaged the reputation of all Dunedin students, and such behaviour can't be tolerated.
Police are monitoring State Highway One between Christchurch and Dunedin for participants.
Otago University Students' Association is also concerned about the rally.
President Simon Wilson says they could be hard to spot, as most revellers are believed to be travelling in undecorated vehicles.
He says, traditionally, it's the Saturday party on Castle Street that gets out of hand.
He hopes any participants will head to town to drink, rather than party in the streets.