Oxfam America has threatened to sue the Securities and Exchange Commission (SEC) if it does not "swiftly enact a new rule" on oil and mining disclosure mandates.
The SEC has set a March 2015 deadline for its first draft on the rules, which force oil, gas and mining companies to disclose payments to foreign governments.
A rewrite of Section 1504 is required under the 2010 Dodd-Frank financial reform law and has been the focus of a lobbying and political battle between oil companies and human rights groups.
"The Commission failed to enact a Final Rule for more than two years," the letter states.
"We insist that the Commission commit to enacting a final rule implementing Section 1504 by December 31, 2014," the letter adds.
If SEC doesn't commit before Aug. 1, to finalizing the rule by year's end, then Oxfam "intends to promptly return to court to enforce the Commission’s legal obligations."
The threat comes one month after 58 House Democrats urged the commission to speed up its timeline for proposing the new rule.
"Resource revenue transparency allows shareholders to make better-informed assessments of risks and opportunity costs, threats to corporate reputation, and long-term prospects of the companies in which they invest," Democrats wrote in June.