The measure, promoted by the absolute majority in both parliamentary chambers of the ruling Morena party, has been described as authoritarian by opposition parties.

The Mexican Senate approved on Friday a reform of two articles of the Constitution to ensure the "unchallengeability" of the reforms to the constitution, a measure that is described as authoritarian by the opposition and that would protect deep legal changes, such as the recently approved one to the judicial apparatus.

The ruling, which was approved in a session that ended in the early hours of the morning and which must be ratified by the Chamber of Deputies, involves changes to constitutional articles 105 and 107 and was rejected by opposition senators with signs and slogans of "No to the dictatorship."

The reform is intended to ensure that the judiciary cannot reverse a package of constitutional changes that the ruling Morena party and its allies are pushing through Congress thanks to the large majorities they have in both chambers after the June elections.

The most controversial is the renewal of the judicial apparatus, which involves the election of thousands of judges and magistrates by popular vote and which has frightened the markets and hit the local currency, the peso.

"The probability of credit rating cuts is also increasing due to the deterioration of Mexico's institutional profile. Overnight, the Senate approved the reform to protect constitutional reforms," Banco Base said in an analysis note on Friday.

Monex Grupo Financiero, for its part, said that the peso was being "affected mainly by local political noise and the electoral factor in the United States," reporting that the Mexican currency was joining other currencies of emerging countries that were experiencing losses against the US dollar.