Rio's Archbishop Orani Tempesta made the announcement July 25.
As many as 1.5 million people are expected to attend the events, both to be led by Pope Francis.
Organizers had provided bathroom facilities and security for up to 900,000 to camp out at Guaratiba the night of July 28. According to local media reports, church officials will now ask participants to go home for the night rather than camp out on Copacabana beach.