WASHINGTON — Looking to instill discipline among Democrats, a coalition of labor, trial lawyers, and liberal groups is launching lobbying and campaign organizations this week to keep Democratic lawmakers from straying on populist issues.

Democrats who don’t hew to this agenda could find themselves facing well-funded primary opponents — an aggressive strategy to counter moderate and conservative blocs within the party.

The groups have organized as two entities — a lobbying wing called They Work For Us and a campaign arm called Working for Us PAC.

“Our PAC will encourage Democrats to act like Democrats — and if they don’t — they better get out of the way,” Steve Rosenthal, one of the coalition’s main organizers, wrote in a memorandum describing the organization.

The new effort is emerging as House Democrats conclude the first stage of their legislative agenda — a two-week rush of legislation that had wide appeal within the party and even among Republicans.

“Now, we move into issues like improving access to health care, fighting jobs moving overseas, protecting rights of workers to organize,” Mr. Rosenthal, who is a leading labor political strategist, said in an interview. “It’s really going to take a very strong effort for Democrats to keep people in line.”

Mr. Rosenthal founded America Coming Together, a political organization that mobilized Democratic voters in the 2004 presidential election.

In addition to Mr. Rosenthal, the two groups are led by some of the most influential organizers in labor and liberal politics, including the secretary-treasurer of the Service Employees International Union, Anna Burger; the executive director of MoveOn.org Political Action, Eli Pariser, and a senior vice president at the American Association for Justice, formerly the American Trial Lawyers Association, Linda Lipsen.

The lobbying arm is organized as a nonprofit organization and already has raised $200,000 toward a goal of more than $3 million for the next two years, Mr. Rosenthal said. It would concentrate on certain key congressional districts to pressure moderate or conservative Democrats to vote with the party’s leadership.

The labor wing of the Democratic Party has been especially frustrated by Democrats who have voted in favor of trade deals that union leaders said hurt American workers by driving jobs overseas. The new political action committee, Mr. Rosenthal said, would be ready to recruit more liberal Democrats to run against them.

“If Democrats in Congress don’t stand strong and fight for the goals we are supposed to share, then progressives need to agitate so they will, or work hard to replace them,” said Donna Edwards, a member of the They Work for Us board who unsuccessfully challenged Democrat Al Wynn, a 14-year House veteran from Maryland, in last year’s Democratic primary.

Keeping the party unified won’t be easy for the House speaker, Rep. Nancy Pelosi of California, as she moves ahead with the rest of the Democratic agenda. Many of the new Democratic lawmakers elected in November replaced incumbents in typically Republican districts. That could make it difficult for many to support some of the party’s stances on economic and social issues.

Mr. Rosenthal said the new coalition would not single out members with moderate to conservative constituencies. Instead, it will target lawmakers who coalition organizers believe are out of step with their voters.

“We’re not trying to force people to the left of their districts,” he said. “We want to make sure that Democrats primarily represent their districts.”