WORKERS TO AND RETAIN THEM IN A SPECIFIC JOB , SET THE RATE OF PAY FOR THAT JOB IN ACCORDANCE WITH THE PARTICULAR EFFORT REQUIRED BY IT .
21 THE COMMISSION CONSIDERS THAT IN THIS REGARD THE DIRECTIVE CONTAINS NO GENERAL LEGAL PRINCIPLE , SO THAT NATIONAL COURTS ARE NOT PRECLUDED FROM BASING THEMSELVES MAINLY OR EXCLUSIVELY ON FEMALE VALUES IF THE PRINCIPLE OF NON-DISCRIMINATION SO REQUIRES IN ORDER TO AVOID DISCRIMINATION AGAINST WOMEN .
22 THE ANSWER TO QUESTIONS ( 2 ) AND ( 3 ), SEEN IN THOSE TERMS , FOLLOWS FROM WHAT HAS ALREADY BEEN SAID IN ANSWER TO QUESTION ( 1 ), THAT IS TO SAY THAT NOTHING IN THE DIRECTIVE PREVENTS THE USE IN DETERMINING WAGE RATES OF A CRITERION BASED ON THE DEGREE OF MUSCULAR EFFORT OBJECTIVELY REQUIRED BY A SPECIFIC JOB OR THE OBJECTIVE DEGREE OF HEAVINESS OF THE JOB .
23 THE DIRECTIVE LAYS DOWN THE PRINCIPLE OF EQUAL PAY FOR EQUAL WORK . IT FOLLOWS THAT THE WORK ACTUALLY CARRIED OUT MUST BE REMUNERATED IN ACCORDANCE WITH ITS NATURE . ANY CRITERION BASED ON VALUES APPROPRIATE ONLY TO WORKERS OF ONE SEX CARRIES WITH IT A RISK OF DISCRIMINATION AND MAY JEOPARDIZE THE MAIN OBJECTIVE OF THE DIRECTIVE , EQUAL TREATMENT FOR THE SAME WORK . THAT IS TRUE EVEN OF A CRITERION BASED ON VALUES CORRESPONDING TO THE AVERAGE PERFORMANCE OF WORKERS OF THE SEX CONSIDERED TO HAVE LESS NATURAL ABILITY FOR THE PURPOSES OF THAT CRITERION , FOR THE RESULT WOULD BE ANOTHER FORM OF PAY DISCRIMINATION : WORK OBJECTIVELY REQUIRING GREATER STRENGTH WOULD BE PAID AT THE SAME RATE AS WORK REQUIRING LESS STRENGTH .
24 THE FAILURE TO TAKE INTO CONSIDERATION VALUES CORRESPONDING TO THE AVERAGE PERFORMANCE OF FEMALE WORKERS IN ESTABLISHING A PROGRESSIVE PAY SCALE BASED ON THE DEGREE OF MUSCLE DEMAND AND MUSCULAR EFFORT MAY INDEED HAVE THE EFFECT OF PLACING WOMEN WORKERS , WHO CANNOT TAKE JOBS WHICH ARE BEYOND THEIR PHYSICAL STRENGTH , AT A DISADVANTAGE . THAT DIFFERENCE IN TREATMENT MAY , HOWEVER , BE OBJECTIVELY JUSTIFIED BY THE NATURE OF THE JOB WHEN SUCH A DIFFERENCE IS NECESSARY IN ORDER TO ENSURE A LEVEL OF PAY APPROPRIATE TO THE EFFORT REQUIRED BY THE WORK AND THUS CORRESPONDS TO A REAL NEED ON THE PART OF THE UNDERTAKING ( SEE THE JUDGMENT OF 13 MAY 1986 IN CASE 170/84 BILKA-KAUFHAUS V WEBER VON HARTZ ( 1986 ) ECR 1607 ). AS HAS ALREADY BEEN STATED , HOWEVER , A JOB CLASSIFICATION SYSTEM MUST , IN SO FAR AS THE NATURE OF THE TASKS IN QUESTION PERMITS , INCLUDE OTHER CRITERIA WHICH SERVE TO ENSURE THAT THE SYSTEM AS A WHOLE IS NOT DISCRIMINATORY .
25 THE ANSWER TO QUESTIONS ( 2 ) AND ( 3 ) MUST THEREFORE BE THAT IT FOLLOWS FROM DIRECTIVE 75/117 THAT :
( A ) THE CRITERIA GOVERNING PAY-RATE CLASSIFICATION MUST ENSURE THAT WORK WHICH IS OBJECTIVELY THE SAME ATTRACTS THE SAME RATE OF PAY WHETHER IT