Montana's largest utility could be penalized up to $1.5 million in fines for being a day late on its tax payments.
NorthWestern Energy spokesman Butch Larcombe says it missed the deadline for property tax bills in all 46 counties where it operates.
The bills, which cover the last six months of 2017, had to be postmarked by May 31. The Billings Gazette reported Tuesday that NorthWestern Energy waited until June 1.
Larcombe says the late payment was due to an error in the company's administrative process.
Montana officials say it's the first time NorthWestern has missed a tax payment deadline, however state law doesn't allow a grace period.
Larcombe says NorthWestern will not fight the penalty for the mistake or pass it on to ratepayers.