Is a referendum necessary to investigate former Mexican presidents?

President AMLO’s proposal to investigate former Mexican presidents for possible past crimes has passed through the Supreme Court and will be scheduled for a vote in Congress amid concerns that the referendum may still be unconstitutional in the first place.
The president has the constitutional power to unilaterally terminate the embargo on Cuba

While the Helms-Burton Act imposes conditions that must be met before the Cuban embargo can be lifted, the president has “the authority to unilaterally terminate the embargo based upon the constitutional primacy of the president’s office in managing U.S. foreign relations.”