I am currently studying an economics case study on protectionist measures but came across a measure which I have not heard off before, one which research has not shed any light on. The case study gives examples of protectionist measures from a range of countries, the one I am confused about reads:
Fuel for official cars in Argentina can only be bought from state-owned oil companies
The protectionist measures such as tariffs and quotas do not seem to apply here. Further research gives this list of protectionist measures, but this doesn't appear to fit in one of those categories either.
Several Google searches have turned up no results either.
My Question: What type of protectionist measure is the example above?