The kidnapping follows the two-day abduction and subsequent release of a former environment secretary in a different part of the jungle a month ago.
The head of the Na Bolom Cultural Association says two activists and two American tourists driving with them were stopped at a roadblock inside the Lacandon jungle by settlers.
Maria Luisa Armendariz said today the settlers surrounded the vehicle Sunday and threatened to burn it or tip it over. They allowed the vehicle to leave yesterday, about 20 hours later.