Legal force may be needed to compel state attorneys general and environmental groups to clarify their climate charges against Exxon Mobil, a House leader said.

Rep. Lamar Smith, R-Texas, the chairman of the House Science Committee, sent a letter to the attorneys general in Massachusetts and New York, and a consortium of environmental advocacy groups, seeking documents tied to charges accusing Exxon of misleading the public and investors about climate change.

Smith said, after requesting information in May, he may issue a subpoena to get access to letters exchanged between the states and environmental groups.

"If you continue to refuse to provide information responsive to the committee's requests on a voluntary basis, I will be left with no alternative but to utilize the tools delegated to the committee by the House of Representatives," his letter read. "Specifically, the committee will consider use of compulsory process to obtain responsive documents in the possession, custody, or control of your office."

Smith in his letter suggested the probe into Exxon may be skewed in favor of a particular agenda and said the extent of the examination so far was "overbroad."

The New York Attorney General's office issued a subpoena to Exxon last year following a series of reports claiming the company was misleading investors decades ago about the potential impact its sector had on the environment.

This year, New York City pension fund managers said they'd move away from coal and the philanthropic arm of the Rockefeller family, which amassed its fortune from oil, said the "morally reprehensible conduct" of Exxon Mobil was in part behind a decision to divest from fossil fuels.

Exxon rejected any suggestion it may have suppressed its own findings into climate change. The company said the accusations were inaccurate, deliberately misleading and charged "activists" with exploiting the issue. The company said its research widely mirrored the global understanding of climate issues at the time.