Environmental and labor lobbies, two key Democratic Party constituencies, have not always seen eye to eye.

“We are strong supporters of domestic oil and natural gas exploration,” said Joe McCartin, who lobbies for the United Association of Journeymen of the Plumbing and Pipefitting Industry. “Not many environmental groups are in favor of that.”

The Senate is set this week to debate the complicated legislation, which could affect a wide swath of the economy. Labor groups are more open to the 490-plus-page bill based on the promise of a prevailing wage for new jobs created by the legislation and more money for training programs.

The consensus on K Street is that the Senate is unlikely to pass the measure, given its complexity and fears that the bill could be a further drag on the economy.

But supporters want to demonstrate as much backing as they possibly can to build momentum for next year. Although President Bush has opposed mandatory greenhouse gas emissions cuts, all three presidential candidates are on record supporting a federal cap-and-trade system.

With Democrats expected to expand their majorities next Congress, labor’s support could prove crucial, especially with big business groups like the U.S. Chamber of Commerce and the National Association of Manufacturers opposing steep emissions reductions and warning of “carbon leakage,” the specific term for outsourcing due to emissions caps.

“Both labor and environmental groups are key constituencies for Democrats, and it happens to be a Democratic majority in the Senate,” said David Hamilton, a lobbyist for the Sierra Club.

Several members being targeted by both sides hail from states with a large manufacturing presence. So it wasn’t surprising that last week environmental groups trumpeted union support, as well as the backing of other newcomers like the U.S. Conference of Mayors and farming groups that have not been major players on the environmental policy previously.

McCartin’s plumbing and pipefitting union wrote the Senate that the bill “will provide the right economic incentives” and create “thousands of jobs in the plumbing and pipefitting industry each year.”

The 13 national and international unions that make up the Building and Construction Trades Department also endorsed the bill.

“We are significantly more organized heading into the fight,” said Jeremy Symons, who directs the climate change program for the National Wildlife Federation. “The coalition has been growing.”

Environmental groups and Democratic leaders have striven in particular to win labor’s backing.

“We’ve had a whole series of discussions with a variety of unions,” Hamilton said. “We’re trying to figure out where we have common ground.”

To draw in more labor support, Democratic leaders sweetened the pot. As revised by Senate Environment and Public Works panel Chairwoman Barbara Boxer (D-Calif.), the bill now includes language that applies Davis-Bacon, which requires workers be paid a prevailing local wage, to certain projects funded by the bill.  

It also would direct millions of dollars to “green-collar” training programs run by unions.   

The campaign, as Hamilton acknowledges, hasn’t been a total success. Some unions remain opposed to a measure sponsored by Joe Lieberman (I-Conn.) and John Warner (R-Va.) that will be debated this week on the Senate floor.

The Lieberman-Warner bill calls for greenhouse gas emissions to be reduced by as much as 65 percent over the next four decades. Industries would be given allowances that would cover one ton of carbon emissions and an overall limit on how much carbon they could emit. Some of the allowances would be distributed for free, but companies would have to buy additional allowances in an auction.  

Phil Smith of the United Mine Workers of America, which counts 105,000 members, said the union opposes the bill. It favors instead a much less aggressive climate bill crafted by Sens. Jeff Bingaman (D-N.M.) and Arlen Specter (R-Pa.).

Smith said the Lieberman-Warner bill, revised by Boxer, would force utilities to abandon coal in favor of natural gas and nuclear power.

“This impacts our members’ jobs,” he said.

The union, along with coal producers and users, wants to allow more time for the technology that would capture and store carbon dioxide emissions from coal and other fossil fuel plants underground to be developed. Only when it has been, critics suggest, should hard emissions cuts kick in.

Scott Segal, a coal industry lobbyist, said the bill would encourage “fuel switching” from coal to natural gas and nuclear power and won’t stimulate the type of innovation needed to curb greenhouse gas emissions without causing a sharp spike in energy prices.