The U.S. Equal Employment Opportunity Commission closed out 2013 with a key win in EEOC v. Mach Mining, persuading an appeals court that the agency’s targets can’t second-guess its prelitigation conduct. Now the EEOC is facing a much bigger test at the U.S. Supreme Court.

The Supreme Court agreed Monday to weigh in on the EEOC’s gender discrimination lawsuit against Mach, an Illinois-based coal mining company. Mach’s lawyers urged the justices to take the case in February, arguing that the EEOC didn’t live up to its unique statutory duty to “conciliate in good faith”—i.e., to try to resolve a dispute fairly before filing suit. The U.S. Court of Appeals for the Seventh Circuit shut down Mach’s line of attack in December, favoring limited judicial review of the EEOC’s conciliation efforts.