Where are the Regulations on International Data Roaming Fees?

I have a 5 GB tethered data plan with AT&T which costs me $50 monthly. Whenever I travel to Canada, AT&T texts me about roaming costs.

The cost of using my full data allowance while roaming without an additional subscription fee would be $78,643.20. That’s 1,024 MB per GB x 5 x $15.63 per MB.

I guess an an illusory democracy controlled by oligopolies, that seems pretty fair.