 US star Lenny Kravitz is scheduled to play in Brazil on Saturday |
Police claim they do not have enough officers to guarantee crowd safety at the open-air gig on Copacabana beach.
Brazilian promoters of the event, the only free show in the series of global concerts highlighting climate change, are hoping to overturn the decision.
The Rio line-up includes Lenny Kravitz, Macy Gray and Pharrell Williams.
Aside from the US acts, Rio will play host to a number of native performers, including singer Xuxa, reggae rock band O Rappa and rapper Marcelo D2.
A giant beach stage in front of Rio's Copacabana Palace hotel has already been erected, with organisers hoping to attract up to one million visitors.
Second cancellation
However, Brazilian prosecutor Denise Tarin has requested a suspension of the concert saying security efforts by police would be concentrated on preparations for the Pan American Games, starting 13 July.
Eight cities will be holding concerts across 24 hours on 7 July, including London, Tokyo, Sydney and Johannesburg.
In a statement, Brazilian promotion company Mondo Entretenimento said it was "working to guarantee the realisation of this important international event".
It said it had plans to use dozens of observation towers and platforms, as well as police cameras, as part of the security scheme for the event.
If Tuesday's court injunction is not over-ruled, it could spell a second cancellation in the Live Earth series, following the scrapping of a concert in Istanbul because of a lack of sponsorship and interest.
Rio has one of the highest murder rates in the world. At least 1,800 people were killed in the first four months of 2007 in the metropolitan area, official figures show.
Last week, clashes between police and drug traffickers in a slum in the Brazilian city of Rio de Janeiro left 19 people dead.