From a recent Columbia FDI Perspectives paper by Catharine Titi:
... it is time to start thinking about a new balance in a move away from investment treaties’ traditional laissez-faire liberalism toward WTO law’s embedded liberalism, a model whereby liberalization is embedded within a wider framework that enables public regulation in the interest of domestic stability.
Investment agreements -- most particularly European bilateral investment treaties (BITs) --contain some of the last vestiges of international economic law’s laissez-faire liberalism. In contrast with trade agreements, European investment treaties tend to be short documents, single-mindedly focused on investment protection and displaying stubborn laconism where the public interest is concerned. ...
Do BITs really reflect laissez-faire liberalism? I suppose the argument is something like this: Because investment treaties can make it harder to regulate, they promote a vision of domestic governing that has only minimial regulation, and thus is "laissez-faire."
On the other hand, you could also argue that the restrictions on regulation that are contained in BITs reflect standard constitutional and administrative law principles. Thus, they are about good governance and respecting rights more than they are about laissez-faire liberalism.
And finally, you could also point out that rich country governments pushing other governments to sign treaties that allow big corporations to sue these other governments doesn't feel much like laissez-faire. It feels like activist government doing special favors for big business, which is not very laissez-faire.
But regardless of how to characterize these issues, it will be interesting to see if she is right about the following: "to all intents and purposes, a new European treaty model appears to be taking root -- a model that, for the first time in Europe, will address the state parties’ regulatory concerns, as well as incorporate investment protection at the pre-establishment stage."