From an interview with the LA Times:
Q: ... Also, on NAFTA, we've heard that you might support maybe a study and then a report, instead of a wholesale reworking of the agreement right away?
[Obama]: Well look, my economic team is reviewing these issues. You know, I've consistently said on trade issues that I want environmental and labor provisions that are enforceable in those trade agreements.
But I also have said that I believe in free trade and don't think that we can draw a moat around the American economy. I think that would be a mistake.
...
My economic team is going to put together a package on trade and on worker issues that will be presented to me. I don't want to anticipate right now what sequences will be on these issues.