Starting this week, diners who snag a coveted table at celebrity chef Thomas Keller's pricey Manhattan restaurant, Per Se, won't need to worry about calculating a gratuity as they linger over a Valrhona chocolate brownie or glass of vintage port.

They'll pay an automatic, 20% service charge instead — and feed an escalating controversy about how travelers reward those who serve their meals, make their beds and carry their bags in what one expert calls "the most tip-conscious country in the world."

"We tend to think of America as a place where the voluntary tip is king," says Cornell University associate professor Michael Lynn, who has researched tipping behavior for 20 years. "Today, that's not necessarily the case."

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