Finding a new way to make money, social game firm Zynga is announcing an alliance with Citi where it will make a line of exclusive game items available for Citi cardholders to purchase with their rewards program points.

The deal follows on the heels of a similar arrangement with American Express. With as few as 600 Thank You Rewards points, users can purchase physical gift cards or virtual currency to be used in Facebook games such as FarmVille, FrontierVille, Mafia Wars and Café World.

The deal is good for Citi because it has a lot of users who don’t participate in its rewards program because they don’t have enough points to spend on anything. By creating low-cost items with Zynga, Citi can make those users more active and motivate them to use the program more. It also encourages the users to give gifts to friends.

Citi started the Thank You Rewards program in 2004. Members can earn points from across a range of Citi businesses, from checking accounts to everyday banking. Zynga has more than 215 million monthly active users playing its games, mostly on Facebook.