Maine Governor Janet Mills has signaled support for a two-percentage-point increase to the state's top income-tax rate for millionaires, a move that would position Maine as having the highest top income-tax rate in New England. The proposed change would raise Maine’s top rate to 9.15%, surpassing Massachusetts (9%) and Vermont (8.75%).

The Democratic governor's current stance represents a shift from her previous positions. In 2024, Governor Mills vetoed legislation that would have increased the top rate to 8.45%. During her 2022 re-election campaign, she stated she was "not interested in raising taxes." Despite state revenue increasing 11% since 2024 and an updated revenue forecast in December showing an additional $248 million, Governor Mills now states her support for the millionaire's tax increase is intended to "give money back to the people" through increased transfer payments.

This policy adjustment comes as Governor Mills competes in the June 9 Democratic Senate primary. Polls indicate she trails Graham Platner, an oysterman who has received an endorsement from Senator Bernie Sanders. Mr. Platner has gained traction among progressive voters by advocating for policies such as a wealth tax and Medicare for All.

In addition to the tax proposal, Governor Mills is backing a bill that would prohibit new data centers in Maine. This issue has become a focal point for some progressives, with Senator Sanders and Representative Alexandria Ocasio-Cortez calling for a nationwide moratorium on new data centers. Proponents of such bans argue that data centers contribute to rising electricity rates.

Conversely, critics suggest that other factors, such as green energy policies leading to the shutdown of coal and nuclear plants, are primarily responsible for electricity supply shortfalls and higher rates. They argue that new data centers could strain the electrical grid if not adequately supported by reliable baseload power. Alternative approaches proposed include requiring large AI companies to build their own power generation facilities or agree to electricity curtailments during grid emergencies. A nationwide moratorium, some contend, could hinder economic competitiveness in the artificial intelligence sector.

Maine currently has some of the highest electricity rates nationally, which has resulted in limited data center investment in the state. Maine’s appointed public advocate stated in January that "to date, there has been very little data center development activity in Maine, and nothing related to data centers has had any impact on Maine’s electricity prices yet." The debate over data centers continues to be a prominent theme within the Democratic Party.