A group of nonprofits is petitioning Montana’s utility board to tighten its oversight of NorthWestern Energy, arguing existing customers could foot the bill for the utility’s plan to provide data centers with electricity. Nine groups working on energy, conservation, social justice and affordability issues on Tuesday asked the Public Service Commission to impose rules on NorthWestern so its 413,000-plus residential customers won’t be forced to shoulder the cost of new power plants and