Starbucks Corp on Monday announced changes to its North American loyalty program that will mean some customers will have to spend more money at the coffee chain to earn free food and drinks.

Under Starbucks' current rewards program rules, customers earn redeemable points for every purchase. The new program will award points for every dollar spent, a change that is sure to spark complaints from customers who are used to accumulating points with frequent purchases of drip coffee and other lower-cost items.

The widely anticipated change from the Seattle-based company comes as airlines and other companies have been tweaking their rewards programs to make them generally less generous to consumers.

Starbucks customers now earn one "star" per purchase and may redeem 12 stars for a free food and drink item. Starting in mid-April, customers will get two stars for every $1 spent and need 125 stars to get a free item.

Matthew Ryan, Starbucks global chief strategy officer, said the change was not a way to weaken Starbucks' rewards program.

However, he acknowledged that 1 percent of the chain's total transactions now come from customers who request two or more transactions to earn stars more quickly.