The European Commission has been working on plans to open up the market for replacement spare parts such as doors, bumpers and windscreens. They do not apply to "non-visible" parts, such as engines, or to the original components in cars.
But car manufacturers argue that the proposals, which would give independent manufacturers the rights to sell their products throughout the European Union, could jeopardise safety, employment and intellectual property, as well as profits.
At the start of this month, four industry chief executives were given a promise by Romano Prodi, Commission president, to give the proposals further consideration - even though Frits Bolkestein, single market commissioner, is keen to see them proceed.
Yesterday, it emerged the proposals, which will need to be approved by EU member states and the European parliament, have been put back until September 7.
This raises the possibility that the legislation could be further delayed until after October - when Bolkestein leaves office.
The carmakers say that 50,000 jobs in the car industry are at stake. They also believe €2bn (£1.3bn) of revenue would be lost to the industry.
The manufacturers also accuse Brussels of failing properly to analyse the impact of the change.
The Commission argues that it needs to balance the needs of intellectual property and competition and provide an equal footing for independent parts manufacturers throughout the EU.