The Transportation Security Administration on Monday delayed a controversial policy change that would have allowed small knives to be carried onto airplanes for the first time since September 11, 2001.

The decision, announced in a letter to TSA employees after a week of heightened security tensions following the Boston Marathon bombings, was greeted with cautious relief by flight attendant unions, which have been waging a high-profile campaign to overturn the plan.

"The 90,000-member Flight Attendants Union Coalition, which has opposed the TSA's ill-advised plan from the start, remains resolute: no knives on planes ever again," the group said in a statement.

Last month, the TSA said that starting on Thursday, it would allow folding knives with blades 2.36 inches (6 cm) or shorter, to be carried onto airplanes, as well as hockey sticks, golf clubs, ski poles and billiard cues.

The agency had determined that these items would not pose a catastrophic threat to an aircraft, and confiscating them from passengers in airport security queues was distracting security officers from screening for greater threats, such as non-metallic explosive devices.

Hijackers in the September 11 attacks used small knives to attack crew members and gain control of aircraft. Cockpits on commercial planes have since been required to have locked doors during flights.

But flight attendants have argued that they could be put at risk from knives carried onto planes and have sought input into the TSA's decision.

"By delaying this policy, the TSA is taking a solid, common sense step in the direction of safer skies," said Senator Charles Schumer, a New York Democrat and one of several lawmakers working with the flight attendants.

"This delay acknowledges that permitting knives on planes is a bad idea. Now the TSA should go the rest of the way and end this flawed policy altogether," Schumer said. – Reuters