  We point out that if neutron--antineutron oscillation is observed in a free
neutron oscillation experiment, it will put an upper limit on the strengths of
Lorentz invariance violating (LIV) mass operators for neutrons at the level of
$10^{-23}$ GeV or so, which would be the most stringent LIV limit for neutrons.
We also study constraints on $\Delta B=2$ LIV operators and find that for one
particular operator degaussing is not necessary to obtain a visible signal. We
also note that observation of $n-\bar{n}$ oscillation signal in the nucleon
decay search experiment involving nuclei does not lead to any limit on LIV
operators since the nuclear potential difference between neutron and
antineutrons will mask any Lorentz violating effect.
