American Express and Bill.com are partnering on a Vendor Pay service, which allows streamlined bill payment on corporate or virtual cards.

The service lets companies make payments with an American Express business or corporate card, without having to open up an account. The service will help improve working capital and cash conversion cycles and provide better data for payment reconciliation, according to a press release.

The service uses single-use, virtual account numbers for added security. The basic service is free for the first user. An enhanced version offers additional services, including synchronization with accounting software and other features, for a monthly fee.

"As businesses grow in size, their accounts payable needs become more complex, driven by more vendors and more invoices," E. Bai Koo, executive vice president, American Express Global Commercial services, said in the release.

American Express is an investor in Bill.com through Amex Ventures.