Here's the NFL statement on the matter:
"However, NFL game officials are charged with protecting the integrity and competitive fairness of the games and club staff members, like players and coaches, have a clear obligation to cooperate in this effort and comply with the direction of game officials. As a result of the failure of club staff to follow the directive of a game official to immediately surrender the towels when directed to do so, and to attempt to conceal the towels, the Chargers have been fined $20,000.
"In order to ensure that products that may have a possible competitive effect are given appropriate review and testing, our office -- after consultation with the Competition Committee -- has advised all clubs that the use of towels or other products that contain any type of adhesive substance is now prohibited on game days until further notice."
The whole story is a little odd. It technically wasn't against the rules to use the towels, but it's no longer going to be allowed. The Chargers didn't gain an advantage, but they were fined anyway.
It will be telling to see if similar towels ever are allowed to be used again. Our guess is the "sticky" towel is out of the NFL for good.