The proposed Townsquare project will increase air pollution and thousands of cars in an already congested area, Alternattiva Demokratika said.
Addressing a news conference, AD chairman Michael Briguglio said "the townsquare project is planned in the middle of an area which is already plagued with heavy traffic flows.
"A revised environment impact study was produced and it confirmed that, as being proposed, Townsquare will increase air pollution and thousands of cars in an area already characterised by overdevelopment at Tigne' Point and Fort Cambridge.
"Indeed, the Townsquare study projects an additional 4,430 vehicles in daily traffic in Qui-Si-Sana, increasing peak flows in the area from the present 24,444 to 28,874 vehicles."
He said that studies commissioned by the developers showed that the development will result in further shading of parts of the Qui-Si-Sana promenade, the sea and the rocky foreshore and will have a major impact on the landscape.
Mr Briguglio said that the silence of Sliema local council on the Townsquare proposal is striking.
"The council seems to be in a total stalemate and is conspicuous in its absence regarding environmental issues in the locality."
Carmel Cacopardo AD spokesman on local government said:
"The Townsquare project should be seen in the light of four important issues, namely the ever increasing number of vacant properties, traffic generation, air quality and traffic generated noise.
"MEPA cannot keep issuing development permits until the number of vacant properties (currently over 70,000) decreases.
"Building more residential units will only serve to increase the number of vacant dwellings. An increase in the number of dwellings on the Tigne' peninsula will also generate more traffic and as a consequence further deteriorate the air quality in the area."
Mr Cacopardo said that Mepa is legally obliged to ensure that the air quality limit values enforced by the Ambient Air Quality Directive are not exceeded anywhere around the Maltese Islands, including Sliema.
Decision makers at MEPA should be held liable if residents of the area suffer adverse health effects.
Sliema residents have a right to air quality which is within the limits specified by the directive and they can petition the European Commission, if their right to clean air quality is not respected by the authorities, he said.