(CNN) -- Mexico's military, the heavy lifter in the country's battle against drug cartels, is under scrutiny following the detention of four high-ranking officers who are being questioned for alleged ties to those same gangs.
The accusations of corruption at the highest levels of the army threaten to erode support from its anti-drug mission, which polls show most Mexicans back. But critics of President Felipe Calderon's militarized campaign against the cartels have argued that the operation precisely makes the military vulnerable to such graft.
All three major political parties in Mexico have asked for a full investigation into reports that the officers were being bribed to protect the now defunct Beltran Leyva cartel.
Neither the federal attorney general's office nor the military has confirmed the allegations, but lawmakers were already lamenting what would be one of the highest-level corruption cases in recent history.
"If proven, the full weight of the law must be applied because they have been federal government officials and are responsible for combating organized crime, and if they are colluding with them the punishment should set an example," legislator Arturo Santana told state-run media.
Retired Lt. Col. Silvio Hernandez Soto was the latest to be brought in to the attorney general's office -- known by its Spanish acronym, PGR -- for questioning Friday. Three generals, including a former deputy defense minister, were brought in for questioning earlier.
All four were brought in for questioning, and so far at least two have been ordered detained for a longer period.
A judge ordered retired Gen. Tomas Angeles Dauahare and active Brig. Gen. Roberto Dawe Gonzalez to 40 days detention while prosecutors continue to gather evidence against them.
The fourth officer, retired Gen. Ricardo Escorcia Vargas, was brought in for questioning on Thursday, and prosecutors have also asked for a 40-day detention.
According to the attorney general's office, the investigation dates back to 2009.
The attorney for Angeles Dauahare, the former deputy secretary of defense, complained that his client's rights are being violated because he has not been able to have access to his file or to his client.
"What I know about his case I know because of what I've read in the media, and from what he's told his wife about the interrogations he's had," Alejandro Ortega said.
The detentions come less than two months before Mexico's presidential election, but the attorney general's office insists there is no political agenda behind the actions.
CNN's Claudia Dominguez and CNNMexico contributed to this report.