Sen. Susan Collins (R-Maine) said Wednesday that she will vote against the confirmation of Scott Pruitt to run the Environmental Protection Agency because “[he] and I have fundamentally different views of the role and mission” of the agency.

“That does not mean that I agree with every regulatory action that EPA has taken,” Collins said in a statement. “At times, the Agency has been difficult to work with and unresponsive to bipartisan congressional concerns. But the EPA plays a vital role in implementing and enforcing landmark laws that protect not only our environment but also public health.”

Pruitt, she noted, had spent much of his tenure as Oklahoma’s attorney general filing lawsuits against the EPA “on numerous issues that are of great importance to the state of Maine,” from regulations on mercury pollution from coal-fired power plants to efforts to cut down on greenhouse gas emissions and cross-state air pollution.

“His actions leave me with considerable doubts about whether his vision for the EPA is consistent with the Agency’s critical mission to protect human health and the environment,” Collins wrote.

Environmental advocacy groups, which have maintained a relentless campaign against Pruitt’s nomination, were quick to praise the news Wednesday.

“Senator Collins has made a courageous decision that puts the health and safety of Maine’s citizens above politics and policy,” Fred Krupp, head of the Environmental Defense Fund, said in a statement.

Still, Collins appears to be the only defection from the Republican Senate majority that is expected to vote in favor of Pruitt’s confirmation as early as this week. If that holds true, her vote will not endanger his confirmation, especially because he is expected to pick up support from at least one Democrat, Sen. Joe Manchin III of West Virginia.

Pruitt’s nomination, like those of other Trump picks, has been contentious from the beginning.

The Trump administration, which did not immediately respond to a request for comment on Wednesday, has praised Pruitt as “an expert in constitutional law” who “brings a deep understanding of the impact of regulations on both the environment and the economy.”

“For too long, the Environmental Protection Agency has spent taxpayer dollars on an out-of-control anti-energy agenda that has destroyed millions of jobs, while also undermining our incredible farmers and many other businesses and industries at every turn,” Trump said in announcing his nomination months ago.

But critics have painted him as a climate-change denier who has spent his time in office serving the interests of oil and gas companies rather than looking out for the health and safety of Oklahoma residents.

Earlier this month, Senate Republicans used their majority to suspend existing rules and push Pruitt’s nomination through the committee level, bypassing Democrats who had refused to show up for a vote. That move set up a full vote in the Senate, which could come Friday.