The Guatemalan Congress on Wednesday approved a law that reduces the punishment for crimes relating to election campaign financing from 12 to 10 years.
The legislation also allows the decade in jail to be commuted to a fine.
The penal reform comes just two days after a UN-backed anti-corruption panel recommended that President Jimmy Morales had his immunity from prosecution removed over corruption allegations relating to the financing of his successful election campaign.
The opposition lawmaker and Together for Guatemala Party's leader, Nineth Montenegro, said she was surprised by what was presented as "urgent" on Wednesday, because "they have never talked about the issues that were approved today".
The US Embassy in Guatemala on Wednesday also criticized the reform, saying on its Twitter account that the Guatemalan Congress had shown no urgency regarding issues such as schools, highways or hospitals, but instead prioritized the reform of "the crime of illicit electoral financing" as "national urgency."
The Public Prosecutor's Office and the United Nations-backed International Commission against Impunity in Guatemala (CICIG) accused the Guatemalan president of hiding information on the funds received by the National Convergence Front (FCN-Nacion), an organization presided over by Morales during the 2015 presidential campaign.