(Reuters) - Amazon.com Inc said on Tuesday it would offer a discount on its popular Prime subscription service for shoppers who receive U.S. government aid, taking aim at a key customer base for rival Wal-Mart Stores Inc.

Amazon said it would offer the $10.99-per-month or $99-per-year Prime service — which includes fast shipping as well as streaming of movies and TV shows — for $5.99 per month to those receiving government assistance including welfare and food stamps.

The online retailer’s move directly challenges Wal-Mart — the biggest beneficiary of the Supplemental Nutrition Assistance Program (SNAP) — where at least one in five customers pay by food stamps.

Prime subscriptions have been key to Amazon’s retail growth strategy, as the service encourages shoppers to buy more goods, more often.

Customers with valid Electronic Benefits Transfer (EBT) cards receiving aid from programs including SNAP and the Temporary Assistance for Needy Families (TANF) program will qualify for the discount, Amazon said.