I'm no expert on this particular issue, but I would guess that the FTC has the authority to impose regulation against things like this. If so, then, if everything were functioning well, there wouldn't necessarily be any need to change laws.
It's also possible that it's already a tort, or can relatively quickly be established as tort by the outcome of a lawsuit like this.
In general, Congress isn't where you go first; Congress is where you go when all else fails and you're willing to take your chances putting a decision like this to a bunch of people whose paychecks are, to an approximation, paid by the companies with the deepest pockets.
But on that note, if someone from the Executive branch wants to try to prosecute GrubHub for this, I'm all for it. Highly unethical at the very least.