The USGA and R&A want the act of green-reading to remain an art form.
Golf's governing bodies on Monday released a joint statement, saying they are "concerned about the rapid development of increasingly detailed materials that players are using to help with reading greens during a round."
"The R&A and the USGA believe that a player's ability to read greens is an essential part of the skill of putting," the statement read. "Rule 14-3 limits the use of equipment and devices that might assist a player in their play, based on the principle that golf is a challenging game in which success should depend on the judgment, skills and abilities of the player."
The statement said they will review "the use of these materials to assess whether any actions need to be taken to protect this important part of the game. We expect to address this matter further in the coming months."
In March, the USGA and R&A unveiled proposed rules changes for 2019, but Ian Poulter, for one, took an opportunity to address what he believed was another ongoing problem, the use of green-reading books, which provide detailed maps to help pros navigate tricky greens.
"The tour greens books should be banned," he wrote. "No one on Tour got a Tour card because of those books. The art of putting has been lost. If you can't read a green, that's your fault."