HELENA, Mont. (AP) -- NorthWestern Energy's proposed transmission line between southwestern Montana and southeastern Idaho has been dealt a potentially fatal blow.

The company says the Bonneville Power Administration notified them that it won't use the proposed $1 billion Mountain States Transmission Intertie to serve BPA's southern Idaho loads. Market uncertainties and environmental issues have also hampered the project.

NorthWestern Energy announced Wednesday that it may have to write off up to $24 million it has spent on survey and investigating costs for the proposed 430-mile power line.

In July, the company said if an agreement with the BPA was unlikely, it may have to abandon the project.

NorthWestern said Wednesday it would continue to monitor market conditions and evaluate options related to the MSTI project.

Copyright 2012 The AP.