What is good for goose is good for gander – The original meaning is that different sexes should be treated the same. The extended meaning is that there should be no doube-standard [UsingEnglish]

It comes from an earlier proverb (nowadays less commonly used): what is source for goose is source for gander [bartleby]. Here is an example (from BBC).

The news says that the current situation in South Ossetia sparks deep worries among western countries for a new cold war with Russia. While almost all western leaders have been condemning Russia, there is a different voice from the former British ambassador to Yugoslavia, Sir Iva Roberts.

He said: “Moscow has acted brutally in Georgia. But when the United States and Britain backed the independence of Kosovo without UN approval, they paved the way for Russia’s ‘defence’ of South Ossetia, and for the current Western humiliation.

“What is sauce for the Kosovo goose is sauce for the South Ossetian gander.”