A quick look at Wikipedia indicates that there is not a dispositive case on the issue. Here's part of what is said there:
"Faithless electors
Main article: Faithless elector
A faithless elector is one who casts an electoral vote for someone other than whom they have pledged to elect, or who refuses to vote for any candidate. There are laws to punish faithless electors in 24 states. In 1952, the constitutionality of state pledge laws was brought before the Supreme Court in Ray v. Blair, 343 U.S. 214 (1952). The Court ruled in favor of state laws requiring electors to pledge to vote for the winning candidate, as well as removing electors who refuse to pledge. As stated in the ruling, electors are acting as a functionary of the state, not the federal government. Therefore, states have the right to govern electors. The constitutionality of state laws punishing electors for actually casting a faithless vote, rather than refusing to pledge, has never been decided by the Supreme Court. While many states may only punish a faithless elector after-the-fact, some such as Michigan specify that his or her vote shall be cancelled.[20]
As electoral slates are typically chosen by the political party or the party's presidential nominee, electors usually have high loyalty to the party and its candidate: a faithless elector runs a greater risk of party censure than criminal charges.
Faithless electors have not changed the outcome of any presidential election to date. For example, in 2000 elector Barbara Lett Simmons of Washington, D.C. chose not to vote, rather than voting for Al Gore as she had pledged to do. This was done as an act of protest against Washington, D.C.'s lack of Congressional voting representation.[21] That elector's abstention did not change who won that year's presidential election, as George W. Bush received a majority (271) of the electoral votes. "
What the state legislatures are doing here is actually disenfranchising voters of their own state in favor of voters in another state will have established the majority for a candidate. That is significant because a situation as occurred in 2000 might well occur again in which the minority candidate wins the most electoral votes. A situation that this reform is designed to prevent. But do not the voters of this state who voted for the minority candidate have a right to have him elected if their own electoral votes would have put them over the top in the College?
If they do not, why bother conducting an election in that state? The Secretary of State for such a state in question simply waits until 49 other states have established the majority candidate and certifies the election for that candidate within the subject state. This argument holds until enough states adopt this rule which make it impossible to determine a majority.
Finally, there is the argument that the Constitution calls for electors not legislatures themselves directly to determine the winner in the state. This proposed reform entirely goes away with the function of an elector. Presumably they had a function or they would not have been inserted by the framers into the process. The argument is that the legislatures cannot take away that function-whatever it is.
