I don’t believe that an employee’s salary may decrease but it’s more on the rate will increase especially if you are doing excellent in your job title. Maybe you are trying to say that his salary now is likely struggling to cover all the bills and expenses due to rising prices of goods and services which I think is understandable due to rising inflation. Well, your friend is not alone, as I bet everyone here has experienced that. Having a side job is the key so that if your main job salary is not enough, you still have another job that you’ll expect to pay you.
That's what he trying to say. The value of the salary now has gotten lower and the only way to deal with the rising cost of prices of bills and food expenses is to have an increase salary and at the same time, having another source of income.
But if you're not believing about salary decreasing, this can happen for someone who's in a bad position where their department is going to get dissolved and the company no longer need that employee.
However, as to keep that employee, they can offer other positions but with lower salary so, it's possible.