Johannesburg firm Webber Wentzel Bowens - South Africa's largest practice - has ended its association with Durban firm Shepstone & Wylie and Cape Town-based Findlay & Tait.
Webbers has also said that it plans to open its own offices in Cape Town next March.
The firm's general manager Murray Thompson said that the split was "amicable" and would not affect Maitland & Co, the London firm run jointly by Webbers and Shepstones.
Thompson said that only one of the seven partners working at Maitlands, John Herholdt, was from Shepstones.
Herholdt will continue working for Maitlands, while his primary South African link will be with Shepstones.
He added that his firm's move had been a natural progression.
"Originally there was seen to be a reason for these associations, but now the thinking has changed. As an international law firm, we have decided the way forward is to have a national presence, rather than alliances with coastal firms," he said.
"We needed a greater level of representation than associations could offer to support our client base properly," he added. "It was great while it lasted but things have moved on."
Thompson said Webbers would still maintain its association with black firm Maponya Ledwaba & Mazwai in Pretoria, and may look to establish more of these relationships.