MEXICO CITY — Mexico’s finance minister resigned on Tuesday with a scathing letter that accused President Andrés Manuel López Obrador’s administration of capricious decision-making and conflicts of interest, in a surprise move that could prove a blow to the anemic economy.
The minister, Carlos Urzúa, was widely seen as part of Mr. López Obrador’s inner circle, and served as a crucial reassurance to investors that the leftist president would maintain financial discipline.
In his letter, which he posted on Twitter, he wrote there were many discrepancies in economic policy, some of them because “in this administration public policies have been made without sufficient evidence.”
Mr. Urzúa, 64, accused the administration of placing officials with no knowledge of finance in the ministry, motivated by “influential people” in the government “with a patent conflict of interest.”
Mr. López Obrador appointed Arturo Herrera, the deputy finance minister, to lead the ministry.
The suggestion that people close to the president are corrupt could prove especially damaging to Mr. López Obrador, who won a landslide victory a year ago on the promise to sweep away Mexico’s entrenched graft.
During the presidential campaign last year, Mr. Urzúa, who has a doctorate in economics from the University of Wisconsin, spent months meeting with investors wary of Mr. López Obrador’s populist rhetoric to persuade them that the new government would keep tight control over finances.
Since taking office last December, Mr. López Obrador has been adamant that Mexico would not increase debt. Instead, he has said that his administration would be able to pay for ambitious social programs with the savings earned from rooting out corruption.
In practice, though, the finance ministry has made sharp cuts in spending on other important programs, such as higher education and environmental protection.
In addition, investors have been concerned over Mr. López Obrador’s expensive plans to build a new oil refinery and a train through the Yucatán Peninsula. He also canceled a new Mexico City airport a third of the way through construction, and then spent billions of dollars on repaying bondholders.
The president has halted Mexico’s energy opening to private investment in favor of government spending on Mexico’s debt-ridden oil and electricity companies.
Those decisions have led ratings agencies to revise downward their outlooks for Mexico’s creditworthiness.