For a law enforcement agency that works hard to be invisible, the Federal Air Marshals have been generating a lot of attention lately. On Thursday, two of the agency's several thousand highly trained traveling armed guards were taken into custody in Houston. Although the U.S. Attorney's office would not comment beyond acknowledging that the Air Marshals were arrested by agents from the Federal Bureau of Investigation and the Department of Homeland Security's Inspector General's office, Government sources tell TIME that the two Air Marshals, are allegedly involved with the possession or transportation of cocaine, and may have been paid several thousand dollars to move the drugs.

The marshals, one of whom is a former agent of the Drug Enforcement Administration, will likely appear in court to face criminal charges next week, and will almost certainly be suspended.

The incident comes only two months after two marshals shot and killed a man who claimed—falsely, as it turned out—to have a bomb while boarding an airplane in Miami. Although the official results of an investigation will not be complete until late spring, it is expected to conclude that the agents acted appropriately in their dealings with the passenger.

The arrest in Houston is a shock to an agency that plays an important role in aviation security. Although there have been air marshals flying for decades, on Sept. 11, 2001, the numbers had dwindled to only three dozen agents. After the attacks, the agency was drastically increased in size and many agents were drafted from other law enforcement agencies and local police departments.

New agents were—and are—subject to security screening and background checks similar to other federal law enforcement agencies, which are required to be updated only every five years.

Critics said the rush to expand allowed too many inexperienced men and women into the service, and there were reports of marshals clashing with airline personnel or other law enforcement agents. Aviation sources say the agency has spent the last few years weeding out poor performers, but the arrest of the two agents in Houston is sure to further stoke those concerns.