Do tips perpetuate unfair wages?

Tipping point
Tipping point   

Is tipping the right thing to do, or does it perpetuate an unethical system of low wages for certain jobs?

Eagles running back LeSean McCoy faced major scrutiny when he left a 20-cent tip at a Philadelphia restaurant last week. PYT Restaurant owner Tommy Up posted a photo of McCoy's receipt on Facebook, which went viral and is currently for sale on Ebay. The infamous receipt is being offered on the auction site at the bid of nearly $100,000, approximately 500,000-times McCoy's tip amount.

"While you have no legal obligation to tip, you have a moral obligation to tip," says Randy Cohen, former writer of The New York Times' "The Ethicist" column.

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Tipping used to be a kind, unexpected gesture to thank someone who is traditionally underpaid and could use extra money in exchange for their hard work and service with a smile. In many ways, that's still the case—as the paychecks for service workers still reflect. But now automatic gratuities and enforced service fees have changed the generous gesture to an expected practice.

But whose expense should tipping be?

Marriott Hotels says the decision should be yours. But a new campaign launched by the hotel giant is becoming a lightning rod for criticism.

Read MoreEnvelopes in Marriott hotels invite tips for maids

The campaign, "The Envelope Please," features envelopes to be placed in 160,000 rooms in nearly 1,000 hotel properties in the U.S. and Canada as a way of encouraging guests to tip housekeepers. But some say the expectation that guests will always tip shifts wage expense from the company to the customer.

Tips tipping
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"They are underpaying their housekeepers," Cohen said.

According to Marriott, their housekeepers earn an average of $10 per hour and annual average salary of $22,000 to $30,000—a rate that is above minimum wage and national labor figures.

How much should we give?

Cohen said tipping servers in restaurants, cab drivers and barbers should be standard etiquette.

According to Emily Post, tips are expected for the following common services:

Wait service: 15 percent to 20 percent pretax, and no less than 10 percent for poor service
Bartender: $1 to $2 per drink or 15 percent to 20 percent of the bar tab
Taxi driver: 15 percent to 20 percent of the fare
Hotel housekeeper: $2 to $5 daily with a note marked "HousekeepingThank You"
Skycap: $2 first bag, $1 per additional bag
Salon/Barber: 15 percent to 20 percent