Until recently, the TSA was operating under a very sensible policy: no collective bargaining. Why introduce the possibility of strikes and protracted negotiations to an agency in charge of ensuring the safety of millions of air passengers?

Now, however, TSA head John Pistole has announced that the government will engage in limited collective bargaining if TSA’s employees vote to unionize.

This is a big win for unions, which have seen their membership numbers drop sharply over the past few decades. They can look forward to adding about 40,000 members to their ranks - members who will pay tens of millions in annual dues.

Passengers, though, have little reason to celebrate.

Look what happened in Toronto over the Thanksgiving holiday in 2006. Canadian law allows airline screeners to unionize, and at that time, the Toronto airport union was unhappy with how the talks were going. So they decided to send a little message to government: They started hand-inspecting every single piece of luggage. As planned, of course, this caused huge backups, and many fliers missed their flights.

Finally, to help move people along, managers allowed 250,000 people to board their flights without being screened. Fortunately, no terrorist incident took place. But it was pure luck that it didn’t.

Supposedly, something like this won’t happen here. Some of the typical areas for negotiation, including pay, promotions and transfer policies, are off limits for collective bargaining. Only certain ones, such as employee awards and recognition processes, are fair game. (Which is bad enough. Unions hate merit pay for good performance and are sure to vote to abolish it, even though it helps motivate employees who have rather tedious jobs.)

But unions frequently ignore the law and strike anyway. Plus, the current restrictions are subject to the whim of the TSA administrator. Mr. Pistole could change the policy at any time, or his successor could.

If that happens, look out. Take transfer policies. When a union is involved, it can take weeks to work out all the details necessary to get one employee transferred from one location or department to another. When it comes to air travel, safety concerns often prompt swift changes in personnel. Imagine, now, that the TSA union is involved, and its leaders decide it’s time to twist the screws to gain some concessions.

Will they drag their feet on transfers, even if it means compromising air travel safety? The track record of the National Treasury Employees Union, one of the two unions vying to represent TSA workers, gives us pause. NTEU already represents Customs and Border Patrol (CBP) employees. It has sued the CBP for moving personnel without negotiating first, and the arbitrator ruled in its favor. So unions are already causing gridlock at other agencies.

Sure, we can cross our fingers and hope the current restrictions aren’t changed or ignored. But consider why the policy changed in the first place: union pressure. It didn’t change on a whim. Unions are among the most well-funded special interests around, and they lobbied the Obama administration hard for this change.

“Unions spent half a billion to elect the president,” writes James Sherk, a labor policy expert at the Heritage Foundation, in a recent paper. “They spent more on the mid-term elections than the Chamber of Commerce did. When they speak, Obama listens.”

Now that they’ve won a partial victory, what are the chances they’ll be satisfied? Not very good. They’ll keep pressing until the TSA is completely unionized.

If they succeed, do you think airport lines will get shorter or air travel any safer? Of course not. That’s why Congress should prohibit TSA from collective bargaining.

Otherwise, we can all expect to fly some pretty unfriendly skies in the future.

Ed Feulner is president of the Heritage Foundation (heritage.org).