Preparing For A Wave Of Citizen Suits: Five Key Strategies On The Diligent Prosecution Bar

• Published date: 04 August 2025
• Law Firm: Beveridge & Diamond
• Author: Ms Madeleine Boyer, Bina R. Reddy and Amber Ahmed

As earlier reported, environmental non-governmental organizations (eNGOs) have promised to pursue enforcement where the Biden EPA left off - they have the legal authority to do so under most environmental federal statutes and a growing war chest to see those promises through. See B&D's alert on how companies can prepare for a citizen suit. A jurisdictional element for an eNGO to bring a citizen suit is the Notice of Intent (NOI) to sue, usually 60 days. When the enforcement agency has "commenced and is diligently prosecuting a civil action" within or prior to expiration of the notice period, the citizen suit is barred.

Setting aside the practical and political aspects of commencing and diligently prosecuting the allegations of an NOI within 60 days, the diligent prosecution bar is tricky. The bar is effectuated differently across similar statutes, interpreted differently between jurisdictions, and applied differently to unique factual scenarios. Strategic use of the diligent prosecution bar should be contemplated early. Here are five considerations about the bar:

1. Know your non-compliance.

The diligent prosecution bar only applies to the same violations of the same regulatory standards alleged in the NOI. An EPA or state action involving different instances of the same or similar regulatory violations or involving different chemicals or constituents from those at issue in the citizen suit will not effectuate the diligent prosecution bar. See, e.g., Sanchez v. Esso Std. Oil Co., 572 F.3d 1, 9 (1st Cir. 2009) (government action bars "the violations they seek to enforce in common."). Know your plant's compliance vulnerabilities and whether eNGOs may be targeting a specific plant. A key strategy for eNGOs is to mine publicly available data and compliance reports (such as Clean Air Act (CAA) Title V deviations) as well as EPA and state agency enforcement records (inspection reports). Knowing what is in the...