Brazil's four largest wireless carriers have filed applications challenging plans for an auction of 4G spectrum currently scheduled for June, telecoms regulator Anatel said.

Vivo, a unit of Spain's Telefonica; TIM Brasil, a subsidiary of Telecom Italia; Brazil's Oi; and Mexico City-based regional giant America Movil's Claro filed the petitions separately on Thursday, an Anatel spokesman told Efe without specifying their reasons.

A smaller wireless carrier, Sweden's Ainmt, also has challenged the auction, which is aimed at making available spectrum in the 2.5-gigahertz frequency range for use in fourth-generation wireless networks.

Anatel has until June 5 to rule on their petitions, the spokesman said.

However, Brasilia-based Oi, the country's fourth-largest wireless operator, said it has not challenged the auction plans but rather presented Anatel with a "suggestion" for improving it.

Oi requested that the regulator provide all the competitors with the names of the companies that are not going to compete for two of the lots, a company spokesman told Efe.

Brazil was questioned by the United States and the European Union earlier this month before the World Trade Organization's Committee on Trade-Related Investment Measures due to equipment makers' concerns over the domestic-content demands placed on auction participants.

Brazil is requiring companies interested in participating in the auction to submit a minimum bid of 3.85 billion reais (about $1.97 billion).

According to the selection criteria, the winners of the auction will be determined by the highest bids.

The government wants the winners of the auction to provide 4G wireless technology - whose speeds are up to 10-times higher than current levels - beginning next year in the six host cities of the Confederations Cup soccer tournament, scheduled for June 2013.

They also must provide 4G wireless coverage in the 12 cities that will host World Cup matches in 2014 and then extend coverage to all cities with more than 100,000 inhabitants by the end of 2016. EFE