Catering to its premium credit-card customers, American Express is constructing passenger lounges in airports and will open its eighth in the United States at Philadelphia International Airport this year.

The 6,300-square-foot "Centurion Lounge" will be in PHL's Terminal A West on the mezzanine level, directly above the current British Airways lounge. The opening is tentatively planned for August.

American Express plans to announce Tuesday that Philadelphia and Hong Kong International Airports will be its newest locations.

Amex lounges offer more and fancier amenities than standard airport lounges: private showers; hot food buffets; complimentary drinks with top-shelf liquor brands; staff to help with travel plans; WiFi; and quiet work areas.

"We've continued to see premium-card members traveling through Philadelphia on a regular basis," said Janey Whiteside, senior vice president at American Express. "We've seen a 10 percent increase in air travel into Philadelphia among our Platinum and Centurion card members over the last year.

"Seeing that increase led to the prioritization of Philadelphia as the next location," Whiteside said.

Access to the lounges is complimentary to Amex Platinum and Centurion cardholders, who can bring their immediate families or up to two guests. (Travelers with Amex Green and Gold cards can pay $50 for a day pass, if the lounge isn't crowded.)

American Express began opening airport lounges in 2013 -- in Dallas, Houston, Las Vegas, Miami, New York LaGuardia, San Francisco, and Seattle -- after American Airlines and United Airlines discontinued complimentary entry to airport clubs with the Amex Platinum and Centurion cards.

Now, complimentary access to airline lounges goes to travelers who have the airlines' branded credit cards -- Citi's AAdvantage executive "world elite" MasterCard for American and the Chase United Mileage Plus Club card for United. Passengers without those cards can pay a daily rate to use a lounge, or an annual membership that can cost several hundred dollars.

Delta Air Lines' credit card is with American Express, and the Amex Platinum and Delta Reserve cards continue to provide entry to Delta Sky Clubs.

Airport lounges are coveted by business and frequent fliers as quiet places to work and relax while waiting for flights. The decisions by United and American angered elite Amex cardholders, who pay a $450 annual fee for the Platinum card and $2,500 for the invitation-only Centurion black card.

Philadelphia lawyer Shanin Specter said that since American, with a hub and 400 daily flights in Philadelphia, dropped lounge access for Amex cardholders, he opts to wait for flights at the aircraft gate.

"People who are spending tens of thousands of dollars a year on American Airlines ought to be given access to that lounge without an additional price," he said.

Specter has been to Amex lounges in other cities, and said, "They are super nice," with terrific food and a wide selection of beverages. "Now that the premium cardholders at Amex will have access to a really nice lounge, that's where I'll go."

Since American Express came on the scene with the Centurion lounges, "there is an arms race in lounges," said Brian Karimzad, director of MileCards.com, which compares credit cards that offer travel rewards. "They are definitely a big step up from your run-of-the-mill domestic airline club. American, Delta, and United have all embarked on pretty ambitious renovation projects of their airport lounges."

American is building a new luxury "Flagship" lounge for first- and business- class international travelers in Philadelphia's Terminal A West, currently the location of its Admirals Club. Access will be complimentary. Renovations include more space to relax, private showers, upscale furnishings, more power outlets to recharge personal devices, and additional cold and hot food and beverage options.

"The competition has been great for consumers," Karimzad said. "Everyone is making the lounges look a lot more sparkling."

The downside is lounges have gotten more crowded because they are popular, he said. "I'd say crowds are probably the biggest complaint."