The European Parliament's industry committee wants vehicle manufacturers to get an additional three years to hit the proposed 120 g/km ceiling for carbon dioxide emissions.
The European Commission has proposed the industry, with the exception of manufacturers of larger cars, should comply with this maximum by 2012.
However, the industry committee wants manufacturers to be given significantly more time to adapt their engine and exhaust designs.
Instead, it has proposed a staged introduction of the limit, with 25% of a manufacturer's cars hitting 120g/km in 2012, 50% in 2013, 75% in 2014 and 100% in 2015.
The committee said in a report: 'This flexibility is needed to allow manufacturers the leeway they need for development.'
The proposed changes will need to be approved by the full parliament and the EU Council of Ministers to become law.
However, resistance can be expected from the parliament's environment committee, which will make its proposals on September 9.
Ministers are expected to make the final vote in October.