The paper presents the design of a reference governor that manages directly the state and input references for constrained output regulation problems. In particular, for the class of weakly input redundant linear systems, the proposed method leads to a taxonomy in terms of non-intrusive and intrusive reference models, on the basis of the effect of reference manipulation on the tracking error. While the non-intrusive reference represents the degree of freedom that one can freely select to meet constraint requirements, the intrusive reference is also assignable during transient, but shall be forced to converge to zero steady state in order to achieve output regulation. A numerical example illustrates the advantageous features of the proposed scheme to support the theoretical findings.