The AJ has learned that the Green Party has complained to the EU because it believes the huge proposals will lead to an increase in air pollutants from traffic, therefore contravening a key directive on ambient air quality.
According to the eco-group, Argent's plans also run counter to the London Mayor's Air Quality Strategy and are not consistent with the London Plan.
The party has already written to Mayor Ken Livingstone outlining its concerns.
The letter, which was sent prior to the scheme winning approval in March, reads: 'By allowing this development, the UK would be contravening the Directive and [we] would have to ask the Commission to investigate and take action.
'There is no car-free housing and the high level of car parking will generate traffic in an area which is already in breach of the EU limit values for air pollution.'
Robert Evans, Director of Argent King's Cross, said: 'King's Cross Central has the best public transport accessibility in London and is the right place for high-density, mixed-use development.
'The Camden and GLA planning reports do address air-quality considerations and these reports recognise that the development accords with planning policy. This includes environmental commitments which help make King's Cross Central one of the most sustainable schemes yet to come forward in London.'