The new rule will permit a player or captain to call a 60-second timeout to confer on strategy by pressing a large red buzzer in the team zone courtside.
It can only be used while on serve, and not between first and second serves, with a maximum of one per team allowed during a match.
They will not be used during singles clashes.
"Timeouts initiate a pause in play, it's a time for teams to discuss tactics and strategy and potentially change the momentum of a match," said United Cup tournament director Stephen Farrow.
"We're excited to see how the best tennis players in the world and their teams utilise this new tool."
The 18-team United Cup kicks off the 2025 season from December 27-January 5 in Perth and Sydney ahead of the Australian Open Grand Slam in Melbourne.
Each team features three men and three women, with ties comprising one men's and one women's singles and an often decisive mixed-doubles clash.
A host of the world's top players have signed up, including Iga Swiatek and Alexander Zverev.
