"Automatic gratuity." Isn't that an oxymoron?

We're talking about the 18 percent (or more) that many restaurants tack on to the bill for large dining parties, usually six people or more. Instead of presenting the check for the meal and letting the diners decide how generously to reward the service, the house adds a flat charge.

That practice might be on its way out. Starting in January, the Internal Revenue Service will regard those payments as wages, not tips, which could lead to higher payroll taxes for the restaurants.

Darden Restaurants, owner of chains including Red Lobster, Olive Garden and LongHorn Steakhouse, has dropped the automatic charges at 100 of its restaurants and may phase them out altogether. Others will surely follow. Good riddance.

Even if you generally tip more than 18 percent, automatic gratuities can't help rubbing you the wrong way. Tipping is supposed to be discretionary — nay, voluntary. Some customers have even sued, saying it's not up to a restaurant to say how big the tip should be.

People who work for tips (and their bosses) say the charges are just meant to make sure the workers are fairly compensated. Waitresses, bartenders and busboys rely on tips to supplement their less-than-minimum wages.

Most customers get that. In a recent survey by discount firm couponcodes4u.com, 63 percent said they felt obliged to tip, even for poor service.

An automatic gratuity is not a tip, though. It's a service charge. And often a big one. Yes, large parties are a lot of work. Anyone who's been seated in the same dining room as, say, Grandpa's 80th birthday celebration, knows a big table can keep several servers scrambling, often at the expense of other disgruntled diners.

Big groups can be hard to impress, too. Just getting all the plates to the table at the same time is an underappreciated logistical feat.

True, customers can be arbitrary and demanding. They can take out their frustrations on the waitstaff when the kitchen is to blame. But a restaurant that runs on tips professes to run on accountability. The better the dining experience, the bigger the tip.

Superior service ought to be in the eye — and the pocketbook — of the beholder.