Country A, Country B, and Country C were member states of the World Trade Organisation (WTO).

1. Country A was a major exporter of rice
2. Country B was a major exporter of vegetables
3. Country C, being a non-food producing country, was a major importer of rice and vegetables from Country A and Country B, respectively, for many years

The recent COVID-19 pandemic has, however, caused Country C to discover weaknesses in its food import program for relying 100 per cent on its immediate neighbours for food security. Therefore, Country C decided to diversify its sourcing and produce food domestically when possible. For instance:

1. Country C, notwithstanding the longer distance, decided to import rice from another three WTO member countries.
2. Country C also decided to grow its own vegetables, aiming to produce 50 per cent of the country's demand in 15 years.

To support the policies, Country C launched two measures: First, a 5% import tariff relief for rice imported from the three faraway countries (to offset the higher logistics costs). Second, a 15% sales tax on all imported vegetables to help local vegetable start-up farms be more price competitive in the domestic market.

Two years into the program, Country A and Country B suffered a significant decline in exports as Country C was importing less from them. The two countries intend to request a consultation with Country C under the WTO's dispute settlement body.

Question: Assuming Country C's import tariff relief to the three other countries was a result of a preferential trade agreement (PTA) or generalized system of preference (GSP). Does Country C has violated MFN principle? Support your answer with a GATT Article or demonstrate your answer with a dispute settlement (DS) case.