The petition currently in circulation to force a statewide vote on the National Popular Vote bill would almost certainly be ruled to be unconstitutional by the current Supreme Court.
Article II, section 1 of the U.S. Constitution states, “Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors” to the Electoral College. Similar language in the Election Clause in Article I of the Constitution gives state legislatures the power to determine the manner of electing members of Congress.
In 2015, Chief Justice John Roberts wrote a scathing dissenting opinion when a 5-4 majority of the U.S. Supreme Court ruled that Arizona voters could use the initiative process to bypass the state legislature and establish an independent commission to create congressional districts. Roberts said, “The Court today performs... a magic trick with the Elections Clause. That Clause vests congressional redistricting authority in ‘the Legislature’ of each State. An Arizona ballot initiative transferred that authority from ‘the Legislature’ to an ‘Independent Redistricting Commission.’ The majority approves this deliberate constitutional evasion by... revising ‘the Legislature’ to mean ‘the people.’”
Now that Justice Kennedy has retired, Chief Justice Roberts’ view that “legislature” means “legislature” almost certainly represents a majority on the new Supreme Court.