MEXICO CITY (Reuters) - Struggling to catch up with the longtime front-runner, the two chasing parties in Mexico’s presidential election have become embroiled in a spat over wrapping used to sell tortillas, the popular flatbread made for tacos.

In an “extraordinary urgent session,” Mexico’s electoral authority ordered the center-right National Action Party (PAN) to stop wrapping tortillas with campaign slogans after the ruling Institutional Revolutionary Party (PRI) called foul.

A thin, unleavened bread usually made of corn, tortillas are ubiquitous in Mexico, which will elect a record number of candidates, including the president, on July 1.

The National Electoral Institute said late on Sunday the PAN’s paper propaganda fodder violated the prevailing legal norms because it was not textile-based and was not recyclable.

The institute gave the company responsible for the offending wrappers 24 hours to halt production.

Opinion polls show that leftist Andres Manuel Lopez Obrador holds a commanding lead in the presidential race, with the candidates representing the PRI and PAN - the only two parties to have governed modern Mexico - scrapping for second place.

The election campaign has been marred by unprecedented levels of violence against candidates and politicians.