Applications for naturalization can suffer from the same delays that other immigration applications endure.
For naturalization applicants who completed their interview, Section 336(b) of the INA, 8 USC § 1447(b), provides for a very specific cure. According to the statute:
If there is a failure to make a determination under [INA] § 335 [8 U.S.C. § 1446] before the end of the 120-day period after the date on which the examination is conducted under such section, the applicant may apply to the United States district court for the District in which the applicant resides for a hearing on the matter. Such court has jurisdiction over the matter and may either determine the matter or remand the matter, with appropriate instructions, to the Service to determine the matter.
Basically, if an N-400 decision isn’t made within 120 days of the initial interview, applicants can go straight to a federal judge who can either decide the merits of the application (approve or deny it) or send it back to USCIS with instructions. For instance, the court can order USCIS to decide your application within a certain amount of days.
Once a lawsuit is filed in federal court on a naturalization application, the district court reviews the application de novo (or anew). This means the court is not bound by any prior findings or decisions made by USCIS. This is in recognition of the tremendous value of citizenship rights. Further, many courts have held that once a lawsuit is filed, USCIS no longer has jurisdiction (or authority) to decide the matter, as it now exclusively belongs to the court. Of course, the plaintiff can agree to send the matter back to USCIS to approve or further consider it as part of settlement of the lawsuit.
As a tool for fighting immigration delays, this is a particularly powerful one since it can take decision-making authority away from USCIS. Because individual cases differ and the stakes can be high, it’s best to consult with an experienced immigration litigator when considering this strategy.