What could go wrong?

With little fanfare, the agency best known for airport screenings has vastly expanded its reach to sporting events, music festivals, rodeos, highway weigh stations and train terminals. Not everyone is happy.

T.S.A. and local law enforcement officials say the teams are a critical component of the nation’s counterterrorism efforts, but some members of Congress, auditors at the Department of Homeland Security and civil liberties groups are sounding alarms. The teams are also raising hackles among passengers who call them unnecessary and intrusive.

“Our mandate is to provide security and counterterrorism operations for all high-risk transportation targets, not just airports and aviation,” said John S. Pistole, the administrator of the agency. “The VIPR teams are a big part of that.”

Some in Congress, however, say the T.S.A. has not demonstrated that the teams are effective.