[rcofdayton]

I don’t see anything that allows the states to request a single issue convention. Article V states:
“The Congress, whenever two thirds of both Houses shall deem
it necessary, shall propose Amendments to this Constitution, or, on the Application of the Legislatures of two thirds of the several States, shall call a Convention for proposing Amendments, which, in either Case, shall be valid to all Intents and Purposes, as Part of this Constitution, when ratified by the Legislatures of three fourths of the several States, or by Conventions in three fourths thereof, as the one or the other Mode of atification may be proposed by the Congress ... .”

[Publius]

For over two centuries, Congress has held to two unwritten standards: the Single Subject Standard and the Contemporaneousness Standard. As Congress views it, the states may request a single subject convention, or a general convention open to all subjects. (There are 2 applications for a general convention left over from 1789.) By the basic principles of contract law, the convention is the agent of the states, and the states are the principals. An agent cannot go outside his agency agreement with his principals, and thus a single subject convention would be forbidden by the principles of contract law to go outside its purview. To make sure the purview is understood, when Congress sets the time and place for a convention, it extracts the language from the states' applications and inserts it into the convention call.

Congress has delegated the power of tabulating applications from the states to the Office of the Archivist of the United States. The Archivist maintains a spreadsheet by state (row) and subject (column). When a column reaches the two thirds threshold, now 34 states, the Archivist sends a memo to Congress that it needs to call a convention.

Every member of Congress believes in the Single Subject and Contemporaneousness standards. So do most, if not all, federal judges. So do most law professors.

There is a small minority in the legal profession that believes that the two standards are unconstitutional and that all conventions are general. No state has ever gone to federal court to challenge the two standards. One individual, William Walker of Auburn, WA, did so in 2000, but the federal courts refused to hear his case because he lacked standing. (I spent two years editing Walker's brief in Walker v. US.)

So as it stands, there is a 277 year old unwritten congressional precedent that covers this, and no one has ever been able to adjudicate it.