An environmental group says it's expanding its investment in a Nevada Senate race by nearly six fold.

The League of Conservation Voters said Thursday it plans to spend nearly $1.4 million to support Democrat Catherine Cortez Masto as she seeks to replace retiring Sen. Harry Reid.

The group previously announced it would spend about a quarter-million dollars on her bid against Republican Rep. Joe Heck.

The league plans to send field workers twice to the doors of 152,000 voters in the Las Vegas area. The campaign is the only Senate race that the group's been involved with this cycle, although it's also spent money supporting Hillary Clinton.

League officials said Heck received more than $400,000 from big polluters and opposes environmental legislation including the coal plant-reducing Clean Power Plan.