Bus companies will have to meet strict emissions targets or face fines
Oxford is to become a low-emission zone, the city council has announced.
The new restrictions aimed at reducing pollution apply only to buses. Firms that fail to meet standards could have their licence revoked.
Bus companies said they will have to spend tens of thousands to pay for new vehicles to meet the new clean-air standards.
Restrictions will not apply to cars, vans or lorries and critics have labelled the plans "a waste of time".
Oxford City Council said they have had "long-standing concerns" about the quality of air.
Records show that Oxford often falls below EU standards for nitrogen dioxide pollution and the council said the buses are the biggest culprits.
Councillor John Tanner said: "The county and the city were working very closely together and I think we've come up with a really good scheme.
"When we started we all thought lets put controls on all traffic but when we looked at it we found that if we can bring all the buses up to European standards then we will get rid of 80% of the pollution problem.
"That will bring the level of pollution in the centre of Oxford below the new European legal limit."
Some opponents to the scheme are worried the new measures will mean fare hikes, but Mr Tanner said the only concerns were environmental.
"This is not about increasing fares this is about reducing pollution.
"The good bus companies are already investing for the future and making sure that pollution is at a very low level - because that's what the public expects.
"Nobody wants to pay a cheap fare and then cough their lungs up when they are shopping."
The Green Party wants an electric tram introduced to replace buses and traffic stopped from driving through the city centre.
Sushila Dhall, from the Oxford Green Party, said: "We would allow cars to drive in and out of the city centre but not through it.
"It doesn't cost a great deal of money to change road layout because at the moment what we have are dangerously high levels of pollution in Oxford city centre and the cost to the public, in terms of health issues, has never been calculated."