What are the requirements for a plaintiff to obtain a notice of right to sue in a Title VII action?

"[f]ailure to observe these requirements renders a suit subject to dismissal in the absence of any equitable consideration to the contrary") (emphasis added); see also Pietras v. Bd. of Fire Comm'rs, 180 F.3d 468, 474 (2d Cir.1999) ("Every circuit before us that has faced the question has held that a plaintiff's failure to obtain a notice-of-right-to-sue[ ] letter is not a jurisdictional bar, but only a precondition to bringing a Title VII action that can be waived by the parties or the court.").