  Motivated by recent experiments on Ni(C_{2}H_{8}N_{2})_{2}Ni(CN)_{4}
(commonly known as NENC), we study the electron spin resonance in the critical
high-field phase of the antiferromagnetic S=1 chain with strong planar
anisotropy and show that the ESR spectra exhibit several peculiarities in the
critical phase. Possible relevance of those results for other gapped spin
systems is discussed.
