  We study the entropy production in a macroscopic nonequilibrium system that
undergoes an order-disorder phase transition. Entropy production is a
characteristic feature of nonequilibrium dynamics with broken detailed balance.
It is found that the entropy production rate per particle vanishes in the
disordered phase and becomes positive in the ordered phase following critical
scaling laws. We derive the scaling relations for associated critical
exponents. Our study reveals that a nonequilibrium ordered state is sustained
at the expense of macroscopic time-reversal symmetry breaking with an extensive
entropy production while a disordered state costs only a subextensive entropy
production.
