Starbucks customers can now earn Delta SkyMiles

Customers at Starbucks can now get more than bonus "stars" for their purchases.

The coffee chain has been collaborating with Delta Air Lines since Wednesday and awards 1 mile for every dollar that is spent at Starbucks as part of an alliance of "two of America's most respected loyalty programs," the companies said in a press release.

To begin earning miles for purchases made at Starbucks locations in the United States, clients have first to connect both their Starbucks Rewards and Delta SkyMiles accounts at a designated website. One more perk: During days on which members are scheduled to fly on Delta flights, members also will earn twice as many stars or reward points for their Starbucks orders.

In order to encourage customers in joining the partnership, participants will receive an extra 500 SkyMiles to link their accounts by December 31, and once they join and make one purchase at Starbucks, members will earn 150 stars, sufficient for a free coffee cup.

The brands have the country's two most popular loyalty programs. Starbucks has over 27 million members in the U.S. and Delta now has about 100 million members around the world (the airline has not revealed figures for the U.S.).

An expansion of Starbucks Rewards has been a company goal as it gives the chain access to customer data and their ordering habits. Members also tend to spend more money on each purchase compared to non-members of the rewards program. This kind of partnership allows Starbucks to increase the company's awareness and stimulate growth, as well as to attract new customers, the chain said in a statement.

The latest Starbucks perk at its loyalty program follows a recent change by competitor Dunkin' to parts of its own bonus program that has caused some outrage among its members.