Transport for London’s plans for the zone involve charging all diesel-engined vehicles over a certain size unless they meet emissions targets.
They include concrete mixers, refuse collection vehicles, lorries and buses.
The scheme is due to come into effect in February 2008 and will become more stringent in 2012.
But Masterlease believes the costs of implementing the plans will outweigh the benefits.
The firm supports the concept, brought in to tackle levels of air pollution in the capital, but has warned that controlling only heavier vehicles mean the plans would be relatively ineffective.
It says a universal approach that includes “excessively-polluting” cars would be fairer.
Masterlease has estimated that the scheme will cost about £520 million. Of that, £130 million will be to run it and £390 million for vehicle operators to comply.
But with the majority of larger vehicles already compliant, the firm says pollution levels will scarcely be reduced.
Head of commercial vehicles Eddie Parker said: “Measures like this may seem extreme but certainly have long-term benefits.
“However, they need to be implemented properly from the start and should not unfairly favour some vehicles over others.
“The other danger is that if central government does not manage this correctly then we could see similar schemes cropping up in other cities.
It would be incredibly confusing if vehicles faced different emission restrictions from one town to the next.”
Mr Parker said that as the scheme was expected to only last for eight years, there were better ways to spend the money.
“The costs are astronomical,” he said.