It seemed like a straightforward question: Should Houston firefighters be paid the same as the city’s police officers? Almost 60 percent of voters said yes.

But now, four months after that vote in November, the mayor of Houston is threatening to lay off up to 400 firefighters to pay for the raises mandated by the ballot measure.

The fight over the citizen-driven charter amendment, known as Proposition B, has exploded into what one expert called a “blood feud” between the mayor, Sylvester Turner, and the union for one of the nation’s largest fire departments, for which the proposed cut would mean about a 10 percent reduction in staff.

Beyond Houston, the situation offers a stark example of the perils of ballot initiatives while providing fuel for employers who warn that higher pay will lead to job cuts.