Publicado en The Wall Street Journal.

Anthony Harrup

Oct. 25, 2018 4:08 p.m. ET

MEXICO CITY—President-elect Andrés Manuel López Obrador on Thursday launched a controversial referendum on the future of the Mexico’s busiest airport, a move that could put his incoming administration on a collision course with investors by canceling the country’s top infrastructure project.

For the next four days, voters can opt to continue construction of a new $13.3 billion airportnortheast of Mexico City that would replace the capital’s existing airport, or scrap it in favor of a less-ambitious option of converting a military base north of the city to complement the existing airport. The new airport is already about a third complete.

For business groups, the referendum represents an early test of Mr. López Obrador’s incoming government, which takes power on Dec. 1. An outcome against the main infrastructure project of departing President Enrique Peña Nieto will signal a negative start for Mr. López Obrador’s administration, some economists say.

“If we have a ‘no,’ I think markets are going to react negatively,” said Marco Oviedo, head of Latin America research at Barclays. “Obviously, if we have a ‘yes,’ the airport bonds will rally, and we’ll see a stabilization of other assets.”

President-elect Andres Manuel López Obrador casts his vote on whether to continue with the $13.3 billion airport to replace the current Benito Juarez International Airport in Mexico City on Oct. 24. PHOTO: EDUARDO VERDUGO/ASSOCIATED PRESS

Discarding the new airport means writing off at least $5 billion spent so far, and could lead to holders of around $6 billion in bonds that were issued to finance the work demanding immediate payment.

The plan to put such a technical issue in the hands of people who know little or nothing about airports has also raised concerns about Mr. López Obrador’s likely governing style. He has vowed a series of referendums during his coming administration, including one halfway through that will ask Mexicans if they want him to step down.

“Trying to make infrastructure a publicly decided issue I think is probably a mistake,” said Jay Jacobs, head of research at Global X, a New York-based sponsor of exchange-traded funds.

“Canceling the development of an airport that could help facilitate more business and tourism for Mexico is going to be negative over the long run.”

Mr. López Obrador, who won the July 1 presidential election by a landslide, called the project designed by U.K. architect Norman Foster a waste of money for a country with Mexico’s social needs. He campaigned in favor of keeping the existing airport and building an international terminal and two runways at Santa Lucía, a military base north of the city.

Business sectors from tourism to airlines say canceling the new airport will ruin a chance to improve Mexico’s airport infrastructure, as the country placed 67th out of 137 countries measured by the World Economic Forum in 2017.

“This new airport is extremely important, not only for tourism activity but also for our country’s economic growth,” said Pablo Azcárraga, president of the Mexican tourism business council.

The referendum, for which 1,073 voting places have been set up across the country, isn’t legally binding. But Mr. López Obrador has said he would follow the voters’ decision. Results of the voting are expected Sunday night.

On Thursday, he defended the vote as an exercise in democracy.

“I understand that there are economic interests in this matter, but we must put the general interest ahead,” he said after casting his vote.

The Center for Advanced Aviation System Development, part of U.S. research-and-development organization Mitre Corp., and the United Nations’ International Civil Aviation Organization say the current, partially completed project is the best option for solving the problem of the current airport, which handled 44 million passengers last year and has no room to grow.

Although the current airport could operate alongside Santa Lucía, it said, the number of flights would be limited by airspace restrictions.

The Mexican College of Civil Engineers also warned of the likelihood of certain airlines, particularly U.S. carriers, placing obstacles and conditions on flying to Mexico City.

“This loss of prestige would not be minor,” it said.

Mr. López Obrador has vowed his government would guarantee the contracts of the main companies working on the new airport, and any work they have been awarded could be transferred to the Santa Lucía military base project, he said this week.

Companies involved in the project include a construction firm owned by Mexican billionaire Carlos Slim, Spanish conglomerate Acciona SA and other leading Mexican builders such as Grupo ICA.

The way the consultation was organized, as well as the way the question was posed, drew wide criticism. Districts chosen for installing voting places won by Mr. López Obrador’s Morena party were far more heavily represented than areas won by other parties, according to a study by Javier Aparicio, a political-science professor at Mexico’s CIDE University.

“I don’t think this is a consultation, I think it’s a farce,” said Valeria Moy, head of the Mexico City think tank ¿México, Cómo Vamos? “The ballots have no security filters, they’re not numbered, anyone can go to any booth they want to vote, you can vote many times.” she added.

Mexico’s Reforma newspaper reported that it conducted an exercise in which it was possible to vote several times at different polling places. Many people on social media reported the same thing.

While the president-elect has refrained from saying which one he thinks people should vote for, his designated communications and transport minister, Javier Jiménez Espriú, and construction entrepreneur José María Rioboó, who is close to Mr. López Obrador, have been playing up Santa Lucía.

The new Mexico City airport was originally expected to cost about $10 billion, although that has since risen to around $13.3 billion as the project was expanded to meet higher expected air-travel demand. The airport won’t be finished until between 2022 and 2024.

Ms. Moy of ¿Mexico Cómo Vamos? said a decision to cancel the airport project would be disastrous.

“You’d be sending everyone the signal that in Mexico you can’t have infrastructure projects that cross administrations, because it will all depend on the governor or president in office,” she said.