SAN FRANCISCO (AP) – One year after failing to win control of the Sierra Club in a bitterly contested election, advocates of stricter immigration limits are back, arguing that the venerable conservation group can best protect the environment by reducing population growth.

The club’s 750,000 members are voting this month on whether the 113-year-old organization should push for tighter restrictions on immigration, and on five seats on the 15-member board of directors, which sets club policy and commands the $100 million annual budget.

Sierrans for U.S. Population Stabilization, a network of club activists seeking to limit immigration, says overpopulation has led to a variety of environmental problems, including increased resource exploitation, the erosion of wilderness and the extinction of species.

“The issue of escalating population growth in the United States is the single most important environmental issue in the nation,” said board member Paul Watson, who also heads the Sea Shepherd Conservation Society. “We’ve got to address this problem.”

But opponents, including many current and former club leaders, argue that wading into the politics of immigration will alienate allies such as labor unions and civil rights groups, and won’t slow population growth worldwide.

“Just to focus on building more walls, and focus on immigration into the United States, does nothing to address the global population problem,” said Sierra Club President Larry Fahn, who is urging members to reject the ballot question. “It would be damaging to the club and its alliances around the country.”

Voting by mail and online is under way until April 25.

Last year’s contentious Sierra Club election drew record turnout after club leaders charged that outside anti-immigration and animal rights groups were trying to seize control of the influential organization.

More than 171,000 members voted – more than twice as many as in previous elections – and the five board candidates backed by the club’s leadership won in a landslide. They defeated some big-name opponents, including former Colorado Gov. Richard Lamm and Frank Morris, former director of the Congressional Black Caucus Foundation.

The San Francisco-based Sierra Club has debated its position on immigration for years, and voted in 1998 to remain neutral.

Still, the club’s immigration control advocates have continued to push for a harder line, saying the U.S. population, which has reached about 300 million people, is expected to more than double this century if nothing is done to slow its growth.

“Our population is already too large to be sustainable within our resource base,” said Dick Schneider, a club member in Oakland who wrote the ballot argument in favor of lower immigration limits. “Unless the U.S. population is stabilized and eventually reduced the Sierra Club will fail in its mission.”

The immigration control advocates insist that they have nothing against immigrants. In fact, they argue that limiting immigration will improve wages and working conditions for immigrant workers by reducing competition for jobs.

“Nobody wants to close the door. We just want to lower the numbers,” said Watson, who is a Canadian citizen and U.S. resident.

Opponents say overpopulation must be addressed globally, by advocating for family planning education, birth control access, fair trade and empowerment of women, especially in poor countries.

“We believe population growth has to be addressed by addressing its root causes,” said Robert Cox, a former Sierra Club president who wrote the ballot argument in favor of remaining neutral on immigration. “Immigration control has done nothing to reduce family size or population pressures. It just scapegoats people who end up bearing the brunt of our trade policies and foreign policy.”

Schneider said he’s not optimistic the ballot measure will pass, but he believes the Sierra Club will have to confront the immigration question eventually.

“The sooner we come to grips with it the better,” Schneider said. “It’s key to protecting the environment.”