Several environmental groups are planning a major climate rally that will draw hundreds of thousands to the National Mall on Sept. 24, the day Pope Francis speaks to Congress and is expected to address the public afterwards.

The permit for the gathering — which will make the moral case for reducing greenhouse gas emissions linked to global warming — is for 200,000 people. The Moral Action on Climate Network, along with the Earth Day Network, League of Conservation Voters, Sierra Club and other groups, have timed the rally on the Mall  the same day of the pope’s speech.  House Speaker John Boehner (R-Ohio) has said the pope “has expressed an interest” in making an appearance on the Capitol’s West Front.

While there has been no official confirmation of formal remarks, Francis is known for making impromptu changes to his itineraries. Federal officials have indicated that the pope is likely to speak for a few minutes to those gathered before the Capitol.

It is unclear whether Francis will focus on climate change during any of his public remarks. However the event represents the latest example of how an array of groups see his visit as a chance to highlight key1 issues he has focused on during his papacy.

In June,  Francis released a major encyclical on the environment, criticizing those skeptical of the link between human activity and climate change for their “denial” of science.

“It must be said that some committed and prayerful Christians, with the excuse of realism and pragmatism, tend to ridicule expressions of concern for the environment,” he wrote in the 192-page document.

Lise Van Susteren, who co-founded Interfaith Moral Action on Climate and whose group originally applied for the rally permit, said in an interview that groups from a wide array of faiths have transcended their other differences by embracing the issue of climate justice.

“Even though many of us disagree so many social issues, the moral issue of climate change is something we are getting behind, with the pope’s leadership,” Van Susteren said.

In September, Van Susteren and officials from other religious environmental groups, including those made up of evangelicals, Jews and Muslims, started discussing the prospect of “a moral march on Washington” in connection with the pope’s visit. The rally has now morphed into a affair that the Earth Day Network, which regularly commemorates the April 22 anniversary of Earth Day on the Mall, is helping orchestrate.

Earth Day Network President Kathleen Rogers, who met with  the pope on Earth Day this year, said the event is in keeping with some of his key interests.

“There’s no question that this pope is passionately, sincerely interested in the poor,” she said, adding, “Climate is incredibly important to him.”

Some close to the church said both the Vatican and environmentalists have to be careful how the encyclical is  portrayed during the trip.

John Carr, a longtime policy director for the U.S. Conference of Catholic Bishops and now director of the Initiative on Catholic Social Thought and Public Life at Georgetown University, said the Vatican isn’t likely to collaborate directly with the event’s planners.

“It’s not helpful to have people delivering the message to be the usual suspects. The goal here is to reach people who have not been engaged. It’s not helpful to have groups that are ideological, partisan, being the ones pushing it,” said Carr. The question for a range of groups looking to connect themselves to the pope’s trip is “will they amplify his message or will they detract by making it seem partisan? People perceived as using the pope and not listening to him will come off badly.”

While details are still being worked out, the rally will last for several hours and stretch between Fourth and Seventh streets on the Mall.