Facebook is testing a $1 charge for users sending messages to people outside their immediate friend circles.
The test kicked off Thursday, part of the company's experimentation with new ways to monetize its user base.
If the sender does not pay the fee, messages sent from outside a user's network will be sent to a lower-priority "Other" folder on the message center page. If the fee is paid, the message goes straight to the recipient's Inbox.
In a statement posted on its site, the social network said research showed "imposing a financial cost on the sender may be the most effective way to discourage unwanted messages and facilitate delivery of messages that are relevant and useful."
Earlier this year, Facebook tested a separate service that allows users to pay $7 to make personal posts more visible in their contacts' newsfeeds.
"This message routing feature is only for personal messages between individuals in the U.S.," Facebook said. "In this test, the number of messages a person can have routed from their Other folder to their Inbox will be limited to a maximum of one per week."
The social network said it would continue to tinker with its message and Facebook Messenger services throughout the coming months.