  I work on a set of Feynman rules that were derived in order to incorporate
the constraint of Gauss's law in the perturbation expansion of gauge field
theories and calculate the interaction energy of two static sources. The
constraint is implemented via a Lagrange multiplier field, $\lambda$, which, in
the case of the non-Abelian theory, develops a radiatively generated effective
potential term. After analysing the contributions of various solutions for
$\lambda$, the confining properties and the various phases of the theory are
discussed.
