(CNN)– A plan by the struggling U.S. Postal Service to raise cash could cost the agency its biggest customer, Amazon. The postal service has a partnership with the online retail giant to deliver some orders to Amazon customers. The contract reportedly brings in about $6 billion a year, wh ich the agency can’t afford to lose. But now, the post office plans to accept bids from other shippers for access to the service’s distribution centers. An Amazon spokesman says the uncertainty might push the company to stop using the postal service as much and that Amazon is evaluating all its options. Categories: News Tags: Amazon, U.S. Postal Service, United States Postal Service, USPS ...read more read less