A major change is about to hit travelers. Some airlines have already instituted it, and it could cost some people their discount fares or even reservations.

There’s probably no perfect timing for the institution of new travel security rules.

The rule about needing a passport (or passport card) for travel to Canada and Mexico was delayed over and over again as the U.S. passport agency got backed up.

In contrast, the liquid rule was instituted overnight. (And every once in a while, I still see a traveler who acts surprised when their water or shampoo is confiscated.)

The latest rule is the new part of TSA’s Secure Flight Program — It requires, no later than November 1, 2010, for all travelers to have their birth dates and legal names entered in the reservation.

And while the program seems to be forgiving about middle names – probably because some people don’t have them – it is unforgiving about birthdates. Which isn’t usually that much of a problem, when a traveler is booking online the site will prompt them for the information, and a travel agent can simply ask.

However, as with most things involving travel, usually doesn’t help when you are the exception.

American Airlines inhibited the ability to issue tickets without Secure Flight information a few weeks ago. United did the same more recently. Southwest hasn’t allowed reservations to be paid by phone without birth dates for months.

It’s a relatively straightforward formula for entering the information too, but it has to be exact. One too many or two few slashes, and leaving off a 0 for example in a birth date, will cause the information to reject. And an error message when an agent tries to ticket.

Already, with some clients we’ve had the problem that someone wants to pay for travel for a new employee, or a job applicant, and we cannot issue the ticket without the Secure Flight data. Not a problem when there’s time to reach the traveler, but when clients call late in the day seven days before travel, and the fare expires at midnight, it’s a different story.

Ditto for vacation travel when many fares, especially bulk fares, must be purchased the same day they are booked. We’ve already had problems where someone wanted to book travel including a family friend or the boyfriend or girlfriend of a college-age child.

So far none of these problems have turned into disasters, but it’s been a short period of time. There’s always the work-around option to put SOMETHING in and then correct it later. This might work with birth dates, but won’t work with names. (Technically, as noted, the system hasn’t required a middle name, but we haven’t had the experience yet of someone going to the airport with a middle name not entered in their Secure Flight data. )

Another issue may be, what happens when the birth date is wrong? Which could happen, especially since many people use European dates with the date then month then year. (Easy to catch fix if your birthday is July 28, harder for a birthday of say June 5.)

In any case, the deadline for all this information is either upon us or very near. If Secure Flight goes as smoothly as most TSA innovations, it’s going to be one heck of an interesting end of the year.