Leading U.S. asset managers have been asked by Republican lawmakers to detail their role in a planned overhaul of the sector's top climate coalition amid concern its efforts amount to collusion, letters to the firms seen by Reuters showed.

The move to seek documents from companies including Capital Group, State Street Global Advisors and JPMorgan Asset Management relates to a planned review within the Net Zero Asset Managers Initiative (NZAM).

After previous pressure led BlackRock to leave the group in January, NZAM asked members to contribute through a series of meetings that U.S. House of Representatives Judiciary Chair Jim Jordan said in the letters could lead to "uncompetitive conduct."

The material is the latest in a series of demands for information and reports by Jordan and his committee suggesting collusion among financial companies. None of the financial institutions called out by Jordan have been charged with breaching federal anti-trust law over their climate efforts, although several face litigation in Texas.

The ongoing political challenge nevertheless has chilled the appetite of U.S. corporate boards to get involved in global efforts to fight climate change and prompted a number to leave coalitions where they could become a target.

The trend has picked up since the election of President Donald Trump, who has called climate change a hoax, targeted a number of green policies enacted by his predecessor and yanked the country out of global efforts to fight climate change.