Organisers warn it is unlikely to be the last such protest.
Transport Minister Annette King yesterday described the proposed protests as "outrageous".
Dunedin demonstration spokesman Peter Sutherland last night said 40 truck drivers had expressed interest in joining tomorrow's protest.
He had received "plenty of support" from Otago transport companies.
Trucks were expected to disrupt Dunedin traffic from 7.30am and converge on the central city at 8.30am, Mr Sutherland said.
Otago-Southland Road Transport Forum representative Murray Maslin, of Wendonside, said about 40 truck drivers indicated they would converge on Invercargill's municipal chambers tomorrow morning.
He warned transport operators would most likely protest again to highlight demands for an inquiry into road user charges.
New Zealand Road Transport Forum chief executive Tony Friedlander said about 1000 trucks were expected to converge on Auckland's central business district from 7.30am.
"[Transport operators] are angry RUC charges have increased by 25% in the last 15 months," he said.
"I don't think there's any more efficiencies we can gain. We are already using fuel-efficient vehicles and driver techniques to keep costs down, so higher costs will have to be passed on."
Increased road user charges introduced on Tuesday affect diesel-powered vehicles and those weighing more than 3.5 tonnes.
Ms King accused the forum of withholding information from the public.
She said this week's increases to road user charges were only the second increase for vehicles over six tonnes since 1989.
Notice of the increases was not given because trucking operators pre-purchased $17.5 million of RUC licences at the old rate when charges increased last year, reducing funding for the Government's roading programme.
Forum research showed an increase of 10% to road user charges would add about 1% to operating costs, she said.
