So what happens if you delay your response? You may be seated, but in all likelihood it will not be with your group because that table is full. Instead, you may find yourself sitting with another, smaller group, or a mixture of individuals and/or couples who have been combined to fill the table. 

When this happens, it is perfectly acceptable to pay a visit to the group table, greet friends and colleagues, or let the higher ups see that you are in attendance. However, it is not okay to switch seats, even if you see an empty chair or two. When you check in at the registration desk, you may ask if the group table is full; if it is not, then you can inquire about changing tables. If it is, accept that you are to sit where assigned -- and stay there!

A friend encountered this situation and asked me how he could have handled the matter. He had confirmed early on that he would be attending an event; upon arrival, he and his partner found the company table where they were to sit and then went off to look at silent auction items. When they returned, they realized their chairs had been commandeered by two co-workers who were supposed to be sitting elsewhere. The two wanted to chat with the company president and took advantage of the fact that their colleague and his guest had stepped away from their seats for a few minutes.

Not wishing to cause an uncomfortable scene, my friend found two available seats elsewhere, but separated from his group, the evening proved to be something of a disappointment.

What could he have done instead? There would have been nothing wrong in choosing to reclaim the correct seats. Lighthearted humor can help to make the point while seeming not to make an issue out of the transgression -- "Thanks for keeping our chairs warm / holding our seats for us!"  Or a more direct "I believe those are our seats" accompanied with a friendly smile, will tell the usurpers it's time to move along.

And if the person/people make it clear they aren't interested in moving?  Then think about who else is sitting at the table -- who may be watching or overhearing this little tableau. A co-worker or colleague? A manager? The company president? A client? The other person's actions will reflect off of them; how you respond to them will speak volumes about you.

Sometimes that other seat may be the better option after all.