Cyclists in Belfast say they will be put in unnecessary danger if 4,000 more taxis are allowed to use the city’s bus lanes.
But a local taxi firm has hit back, saying that the "antagonistic attitude” of some cyclists was the real problem.
As part of a 12-week trial staring on Monday, 4,000 more cabs will be able to use the restricted lanes, already open to cyclists, buses, motorbikes and some types of cab.
Fonacab boss William McCausland told the Belfast Telegraph that some of his drivers had read comments online where cyclists said they would deliberately ride slowly and in the middle of the bus lane.
"All of our drivers are competent and able to negotiate around a cyclist with no issue," he said.
"We recently sent a memo around our drivers to remind them to be mindful of cyclists - but sometimes the cyclists need to be more careful too; this aggression doesn't help anyone.
"At the moment our wheelchair accessible taxis can already use the bus lanes regardless of whether someone with a wheelchair is even in the taxi. It's ludicrous - nobody can justify it.
"You could get one of our Class B taxis drop you off to work one day and it could cost £4.80. The next day you could get a Class A taxi, but because it can't use the lane, you could be sitting in traffic and find the same journey will cost you £6.
"In the city centre lanes it will help our customers. If you're at the Europa and you've got a customer to pick up at City Hall it will make a big difference not sitting in traffic. To a customer, waiting every 20 seconds feels like 20 minutes."
A spokeswoman for cycling body Sustrans said: "Cyclists are among the most vulnerable road users.
“We believe this trial contradicts the Government's own strategy to promote sustainable transport and active travel as it will hinder people to have the freedom and confidence to travel by bicycle for everyday journeys."
After an unpromising start, having to be bribed by her parents to learn to ride without stabilisers, Sarah became rather keener on cycling in her university years, and was eventually persuaded to upgrade to proper road cycling by the prospect of a shiny red Italian bike, which she promptly destroyed by trapping a pair of knickers in the rear derailleur. Sarah writes about about cycling every weekend on road.cc.