The public works ministry has also desisted from using the PPP model for the modernization of Asunción's main airport.
Financing conditions have much improved, the transport confederation says.
The CChC said that the US$600mn project could be financed with funds the city receives in compensation for government funding of Santiago's Transantiago bus system.
While the designated transport and communications minister shared more details about the consultation, a survey by one of Mexico's leading polling firms showed that most Mexicans are not interested in participating.
Concessionaire ABV will have to pay fines imposed by Brazil's civil aviation agency.
Brazil's development bank will finance up to 80% of the required US$2bn investment.
Mayor Enrique Peñalosa said that the full tender will be launched soon, while the contract would be awarded in July or August.
The Chiapas-Mayab railway connects the Mexican cities of Valladolid, Mérida, and Campeche, which are also included in AMLO's proposal for the Maya rail project.