Activist shareholders are pressuring companies such as Nike to pull out of the U.S. Chamber of Commerce, arguing that the trade group’s stance against climate change legislation is incompatible with the companies’ own positions.

Green Century Funds, Newground Social Investment and others sent letters to Nike CEO Mark Parker, urging the company to go beyond its decision Wednesday to step down from the chamber’s board of directors.

“It’s a very positive step and a clear indication the chamber’s recalcitrant position is not supported by its members,— Green Century Funds’ Emily Stone said about Nike’s stepping down from the chamber’s board. “At the same time, we will continue to urge Nike to leave the chamber.—

Green Century Funds holds more than 3,300 shares of Nike stock.

Walden Asset Management, which owns more than 500,000 shares of Nike stock as a division of Boston Trust & Investment Management Co., sent a similar letter to Nike on Wednesday.

“The Chamber’s position and active voice on climate change is especially embarrassing for numerous members who are proactive leaders on reducing greenhouse gases and limiting the negative impact on climate change,— Walden Senior Vice President Timothy Smith wrote.

Nike spokeswoman Erin Dobson said the letters from shareholder groups did not play a part in the company’s decision to withdraw from the chamber’s board of directors.

Nike had been trying to work with the chamber to change its position on climate change for nearly a year, Dobson said. Last week, Nike publicly confronted the chamber on its stance before deciding to leave the board but remain a member of the group.

“We believe that on the issue of climate change the Chamber has not represented the diversity of perspective held by the board of directors,— Nike said in a statement. “We will continue our membership to advocate for climate change legislation inside the committee structure and believe that we can better influence policy by being part of the conversation.—

Nike, which said it would continue to “evaluate— its membership with the association, is just the latest chamber member to take heat from shareholders.

The unrest over the chamber’s policy on climate change has been brewing for the past year as several members have started pro-climate change coalitions, including the Business for Innovative Climate and Energy Policy and the U.S. Climate Action Partnership.

The chamber has also seen three large utilities — Chicago-based Exelon Corp.; California’s Pacific Gas & Electric; and PNM Resources, a holding company with New Mexico ties — exit in the past two weeks.

Environmental activists and union officials are trying to use Nike’s stepping down from the board and the recent defections to drive other companies to do the same.

The Center for Political Accountability and more than a dozen of its shareholder activist groups wrote 25 members of BICEP, USCAP, the National Association of Manufacturers and the chamber in May, raising the discrepancy between the companies’ position on climate change and that of NAM and the chamber. The group followed up with another letter in June, asking the companies to tell the associations to disclose their disagreement on climate change on the associations’ Web sites and to refund a portion of the companies’ dues, CPA’s founder Bruce Freed said.

CPA is in discussion with 10 of the companies on how to resolve the issue on climate change.

“Companies are becoming increasingly sensitive with dealing with the misalignment with their trade associations… and the fact that they need to deal with this,— Freed said. Freed declined to release the names of the companies his group is working with.

Freed said he wouldn’t be surprised if more companies leave the chamber because “climate change is a bottom-line issue.—

Environmental advocates are also targeting companies such as General Electric and Caterpillar — both members of coalitions supporting climate change. But some environmentalists say that getting companies like GE, which relies on the chamber to lobby on its behalf on issues such as trade, are less likely to depart because of climate change.

So far, the chamber hasn’t changed course on climate change legislation because of the departures.

“We represent over 3 million businesses, including virtually everyone in the climate change debate,— chamber spokesman Eric Wohlschlegel said. “The overwhelming consensus among our members, including renewable and alternative energy companies, is we need sensible climate change legislation that will actually achieve what it sets out to achieve: a reduction in green house gas emissions.—