  The nearly 100% linear polarization has been reported for a few fast radio
bursts. This finding places severe limits on the emission mechanism. I argue
that the totally polarized radiation could be generated in the course of
relativistic magnetic reconnection in the outer magnetosphere of the magnetar.
At the onset of the magnetar flare, a large scale magnetic perturbation forms a
magnetic pulse, which propagates from the flare cite outwards. The pulse
strongly compresses magnetospheric plasma and pushes it away. The
high-frequency MHD waves are generated when the magnetic pulse reaches the
current sheet separating, just beyond the light cylinder, the oppositely
directed magnetic fields. Coalescence of magnetic islands in the reconnecting
current sheet produces magnetosonic waves, which propagate away on the top of
the magnetic pulse and escape in the far zone of the wind as radio waves
polarized along the rotational axis of the magnetar. I estimate parameters of
the outgoing radiation and show that they are compatible with the observed
properties of FRBs.
