The United States non-governmental organisation Water Defense, headed by actor Mark Ruffalo, has joined forces with the Treasure Karoo Action Group (TKAG) against hydraulic fracturing.
The coalition said on Thursday that TKAG chairman Jonathan Deal would take up a non-executive director's seat on the board of Water Defense, while Ruffalo would do the same on TKAG.
"We intend to co-operate with and support TKAG on all levels, including ensuring that fundraising efforts are directed where they are most needed," Ruffalo said.
"It is a fact that environmental NGO's have to oppose global giant corporations who have virtually unlimited budgets to push their corporate agendas."
Deal said the coalition was "one of the most exciting accomplishments in the anti-fracking fight".
Hydraulic fracturing, or fracking as it is commonly known, involves injecting a mixture of chemicals into the earth at high pressure to free natural gas.
The TKAG believes this will harm the sensitive Karoo environment and poison underground water.
Fracking is banned or under some form of moratorium or restriction in 108 places and five countries.