GATS doesn't apply tariffs, but
The GATS comes in two parts; firstly a framework of rules, principles and concepts which underlie
obligations regarding measures affecting international trade in services; and, secondly, the specific
negotiated commitments listed in countries' schedules for service sectors. The GATS covers four
modes of supply: (1) ...
If you look at the four different ways that international service trade is categorised by the GATS, that will help you think about what sort of constraints are faced. The four GATS "modes" are:
Cross border (the most simple): a firm in country A supplies a service to customers in country B.
Consumption abroad: someone from country B visits A and uses a ...