Wash. Rev. Code § 81.04.235
All complaints against public service companies for recovery of overcharges shall be filed with the commission within two years from the time the cause of action accrues, and not after, except as hereinafter provided, and except that if claim for the overcharge has been presented in writing to the public service company within the two-year period of limitation, said period shall be extended to include six months from the time notice in writing is given by the public service company to the claimant of disallowance of the claim, or any part or parts thereof, specified in the notice.
If on or before expiration of the two-year period of limitation for the recovery of overcharges, a public service company begins action under RCW 81.28.270 for recovery of charges in respect of the same transportation service, or, without beginning action, collects charges in respect of that service, said period of limitation shall be extended to include ninety days from the time such action is begun or such charges are collected by the carrier.
All complaints against public service companies for the recovery of damages not based on overcharges shall be filed with the commission within six months from the time the cause of action accrues except as hereinafter provided.
The six-month period of limitation for recovery of damages not based on overcharges shall be extended for a like period and under the same conditions as prescribed for recovery of overcharges. If the six-month period for recovery of damages not based on overcharges has expired at the time action is commenced under RCW 81.28.270 for recovery of charges with respect to the same transportation service, or, without beginning such action, charges are collected with respect to that service, complaints therefor shall be filed with the commission within ninety days from the commencement of such action or the collection of such charges by the carrier.
RCW 81.04.235