The small states cannot stop this. All it takes is for the 13 largest states to pass laws like this. Then, assuming it is constitutional, it would go into effect, without a single small state approving it.
In contrast, it takes the approval of 34 (or is it 38) states to pass a Constitutional Amendment. The large state liberals know they cannot get enough small states to agree to pass a Constitutional amendment to remove the Electoral College. That is why they are trying to get their way though the 'backdoor'. And if they can go 'backdoor' for this, can they do so on other things? How long until 13 big states are making all the decisions for this nations?
The 13 largest states can already determine the outcome of a presidential election on their own without monkeying around with the process, so I don't see what they have to gain by it from a collective standpoint.