This paper presents some definitions about of Interval Type-2 Fuzzy Constraints regarding Interval Type-2 Fuzzy Linear Programming models (IT2 FLP) such as the Interval Type-2 Fuzzy Feasible Region (IT2 FFR) and the concept of an Interval Type-2 Fuzzy Constraint (IT2 FC). In this proposal, a LP problem with uncertain right hand side parameters treated as Interval Type-2 Fuzzy sets is theoretically defined. As always, a real-valued solution should be found, so two optimization methods which deal with uncertain right hand side parameters are referred.