FOR many American professionals, the Labor Day holiday yesterday probably wasn’t as relaxing as they had hoped. They didn’t go into the office, but they were still working. As much as they may truly have wanted to focus on time with their children, their spouses or their friends, they were unable to turn off their BlackBerrys, their laptops and their work-oriented brains.

Americans working on holidays is not a new phenomenon: we have long been an industrious folk. A hundred years ago the German sociologist Max Weber described what he called the Protestant ethic. This was a religious imperative to work hard, spend little and find a calling in order to achieve spiritual assurance that one is among the saved.

Weber claimed that this ethic could be found in its most highly evolved form in the United States, where it was embodied by aphorisms like Ben Franklin’s “Industry gives comfort and plenty and respect.” The Protestant ethic is so deeply engrained in our culture you don’t need to be Protestant to embody it. You don’t even need to be religious.

But what’s different from Weber’s era is that it is now the rich who are the most stressed out and the most likely to be working the most. Perhaps for the first time since we’ve kept track of such things, higher-income folks work more hours than lower-wage earners do. Since 1980, the number of men in the bottom fifth of the income ladder who work long hours (over 49 hours per week) has dropped by half, according to a study by the economists Peter Kuhn and Fernando Lozano. But among the top fifth of earners, long weeks have increased by 80 percent.