'major partners' is correct and can be used in written English
Example: We are grateful for the support of our major partners as we embark on this new project.
In the Philippines, he endorsed McDonald's and San Miguel beer, among other major partners.
"I always worried that one of our major partners might drop out on us," he said.
This summer all three of his major partners threatened to quit as the country's economic deficit ballooned.
We could do a deal with the US more quickly, and also with China and other major partners.
Then Addenbrooke's, the world-famous Cambridge hospital that was one of the major partners, was put in special measures.
Lockheed, however, notes that it already has two major partners, the British military contractor BAE Systems and Northrop Grumman.
In China, Star Alliance — one of whose major partners is United Airlines — is considered to have wider presence than Oneworld.
Brazil has long been Uruguay's main trading partner; Argentina and the United States are also major partners.
Trade friction between the United States and its major partners is not uncommon, but the steel measures seem to have struck an unusually raw nerve.
"New administrations always revise the policies of their predecessors," he said, adding that he still considered the United States as "one of our major partners".
As an example, The Atlantic Philanthropies – one of the major partners – is a time-limited foundation which focuses its grant-making on addressing racial disparities in American life.
