Counsel of record is Clark Neilly, who was Alan Gura’s right-hand man in Heller. The most important part of the brief is Part III, which begins: “To enslave a class of people requires three basic things: destroy their self-sufficiency, prevent them from fighting back, and silence any opposition.” The brief then goes on to argue that the the Court should resist suggestions that it hold that the Privileges or Immunities clause makes the first eight amendments applicable against the states, but does nothing else.
Thus, for example, many states adopted laws that kept blacks from practicing trades or even leaving their employer’s land without permission; others adopted vagrancy laws that, in practice, made it illegal to be unemployed, and therefore illegal to look for work
And the animating purpose of the Privileges or Immunities Clause, the elimination of constructive servitude, could not be achieved by enforcing only the narrow set of rights already enumerated in the existing Constitution. This last point is best illustrated by the sheer variety of laws invented by Southern governments to prevent freed slaves from enjoying the personal autonomy that was to have been theirs upon ratification of the Thirteenth Amendment. To take just one example, starting with Virginia in 1870, Southern states began to pass increasingly restrictive regulations of “emigrant agents”—people who attempted to recruit freedmen to leave their plantations by promising higher wages and better working conditions on understaffed Western plantations, eventually making it illegal or practically illegal for people to even offer these economic opportunities to poor workers. Those and other laws had the express (though not always expressed) purpose of binding former slaves to the very same plantations they had worked during slavery, and upon essentially the same terms.
In short, the protection of at least some economic rights (the right to choose where to work, the right to choose not to work, and the right to learn about work opportunities) was among the rights which the Privileges or Immunities clause was specifically intended to protect.
IJ does not ask the Court in McDonald v. Chicago, to take any affirmative steps to protect those rights. The IJ simply urges that the McDonald Court enforce the Second Amendment via the Privileges or Immunities clause, and not create any dicta prematurely restricting the scope of P/I.