Contact Interaction Explanation of HERA Events and SU(3)_Ctimes SU(2)_Ltimes U(1)_Y Invariance

We reexamine the contact interaction hypothesis for excess high-$Q^2$ events seen at HERA in $e^+ p \to e^+ X$ scattering. We consider the most general structure of contact interactions insisting on $SU(3)_C\times SU(2)_L \times U(1)_Y$ invariance. Apart from constraints for $e^+ e^- \to q\bar q$ , Drell-Yan and atomic parity violation experiments, we find stringent constraints from neutrino deep inelastic data. A possible choice of contact terms that escape present bounds is still possible, althought new data from FERMILAB and LEP should further constrain such a possibility.