First, it should be clarified that the wage under labour law, should not be less than the minimum wage, which is held annually indexing, that is changing.
Reducing wages, you change one of the obligatory conditions of the contract. Usually, this change cannot be unilateral. So two months before the introduction of the new wage, will notify the employee. This should be done in writing. In the notice indicate the reasons that caused this decision (note that they must be reasonable). The employee, agreeing with this information, should put his signature.
If you reduce the salaries of several employees at once, it is advisable not to make everyone notice, and to make it one of the documents, after which everyone will sign and date next to his name.
Then make an order on changes in staffing. In this administrative document, specify the position, employees who need to make changes, also write the date of the amendment and the amount of salary.
Then to the introduction of new conditions make an additional agreement to the labor contract, set the new wage and the effective date of the new edition in force. Supplemental agreement, make two copies, one of which will remain with you, and the other with the employee.
Then place your order about the reduction of wages. It will also list the positions, the employees themselves, specify the wage rate, write the basis (order on changes in staffing, additional agreement). This order must also be signed by the employee, which would mean his agreement with the above information.