  We re-visit the problem of New Physics (NP) contribution to the branching
ratio of the $B_s \to \mu^+ \mu^-$ decay in light of the recent observation of
this decay by LHCb. We consider R-parity violating (RPV) supersymmetric models
as a primary example - recently one has reported stringent constraints on the
products of the RPV coupling constants that account for the $B_s \to \mu^+
\mu^-$ transition at the tree level. We argue that despite the LHCb measurement
of the $B(B_s \to \mu^+ \mu^-)$ is in a remarkable agreement with the Standard
Model (SM) prediction, there is still room for a significant New Physics
contribution to the $B(B_s \to \mu^+ \mu^-)$, as the sign of the $B_s \to \mu^+
\mu^-$ transition amplitude may be opposite to that of the Standard Model;
alternatively the amplitude may have a large phase. We conduct our analysis
mainly for the case of real RPV couplings. We find that taking into account the
scenario with the sign flip of the $B_s \to \mu^+ \mu^-$ amplitude (as compared
to that of the SM) makes the bounds on the RPV coupling products significantly
weaker. Also, we discuss briefly how our results are modified if the RPV
couplings have large phases. In particular, we examine the dependence of the
derived bounds on the phase of the NP amplitude.
