American Express announced plans to introduce a co-branded Amazon credit card for small businesses.

The card company said the offering is part of a broader multi-year partnership. It is Amazon's first small business card.

The deal gives Amex a big platform to woo small business customers as it aims to become a leading lender to small and mid-sized companies. Amazon also has a branded card with J. P. Morgan Chase, which issues one for consumers shopping on Amazon's site and elsewhere, and Synchrony Financial.

Small business cards can be highly profitable for banks. While consumers may spend a few thousand dollars a month on credit-cards, businesses can rack up hundreds of thousands of dollars in bills by funneling all their purchases through cards to maximize rewards points.

Amex won the mandate from other banks including J. P. Morgan, which had been competing to partner on the co-branded card earlier this year, according to a person with knowledge of the situation. Amazon ended up going with the leader in this space: Amex says it is the biggest card issuer for U.S. small businesses.

Amazon has been looking to deepen its reach with small business owners by replicating the success it’s had with household consumers. The firm has previously launched a Prime membership program for businesses and has already lent $3 billion to more than 20,000 small businesses that sell on its website, Amazon said last year.

The move comes one day after the U.S. Supreme Court sided with Amex in a lawsuit over merchant fees. The high court said Amex's policy of forbidding retailers from encouraging customers to use rival cards with lower fees doesn't violate antitrust law. The decision was seen as favorable for other companies, including Amazon, that also charge merchants fees to access customers on their sites.

American Express shares were slightly higher on Tuesday.

CLARIFICATION: This story has been updated to delete the reference to Citigroup being one of the banks that had been competing to partner on the co-branded card.