Who needs a law?
They could just ask nicely, like they did with the cell phone companies.
Or they suggest that you might want to keep friendly with government purchasing depts
Or they suggest you might not want a tax audit
Or they simply turn up with lots of guns and some orange jumpsuits and suggest you comply
Now that we know the courts will grant immunity to anyone who illegally cooperates with warrantless wiretaps - why risk upsetting the government ?