Can smokers claim an ADA disability to justify taking lengthy smoke breaks?

Q. I own and run a paper company in Texas. Some of my employees who are cigarette smokers regularly take more breaks than the two, 15-minute breaks that are allowed under their employment contract—and some of the nonsmokers in the office are getting angry. When I confront the smokers about this conduct, I am increasingly hearing them make an unusual claim—that they have a “disability” and are protected by law. What should I do?