[jariel]

"your manager has decided that your work is now less valuable "

No - this is supply and demand. There are two sides to the equation, not one.

Someone working where there is no taxes, and low cost of living, will value the employment opportunity differently.

The 'clearing price' for the 'trade' will thus be different, even when all other factors are otherwise the same (i.e. the workers skills and abilities are identical.)