Exxon Mobil Corp. said it has left the American Legislative Exchange Council (ALEC) following a clash over climate change policy.

The nation’s largest oil and natural gas company did not say why it let its membership lapse.

“We review our memberships on an annual basis and this year have decided to discontinue our membership in ALEC, which expired at the end of June,” Exxon Mobil spokesman Scott Silvestri said Thursday.

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But Exxon Mobil was one of the leading voices against a proposal within ALEC to pressure the Environmental Protection Agency (EPA) to rescind the policy that allowed it to regulate greenhouse gas emissions. The proposal ended up getting scuttled.

ALEC has lost numerous major members over its advocacy against climate change policies, including Royal Dutch Shell, Google and Microsoft. Companies like Ford Motor Co., Expedia Group Inc., Yahoo Inc. and Yelp Inc. have recently left as well, without specifically mentioning climate change.

“The American Legislative Exchange Council values partnership with ExxonMobil and stakeholders across the business community. Organization government relations strategies change over time, and we have valued ExxonMobil’s work and leadership with ALEC on STEM education, among other issues,” ALEC spokesman Bill Meierling said.

The left-leaning Center for Media and Democracy said Exxon Mobil and its affiliates have given more than $1.7 million to ALEC, based on various disclosures by the company and the organization.

ALEC, which has been supported by conservative billionaire brothers Charles and David Koch, does not itself lobby the federal government. Instead, the group’s corporate members use it to push mostly state legislators on various policy matters, often through the use of model legislation to be proposed in statehouses.