AND INVALIDITY INSURANCE INSTITUTION , HEREINAFTER REFERRED TO AS ' ' THE LUXEMBOURG INSTITUTION ' ' ), A LUXEMBOURG SOCIAL SECURITY INSTITUTION , AND TWO UNDERTAKINGS BASED IN FRANCE SPECIALIZING IN CONSTRUCTION WORK AND THE MAINTENANCE OF THE INFRASTRUCTURE OF RAILWAY NETWORKS , SECO SA AND DESQUENNE & GIRAL SA . IN 1974 AND 1977 THOSE UNDERTAKINGS CARRIED OUT WORK OF VARIOUS KINDS IN THE GRAND DUCHY OF LUXEMBOURG . FOR THAT PURPOSE THEY TEMPORARILY SECONDED WORKERS WHO WERE NEITHER NATIONALS OF A MEMBER STATE NOR FROM A COUNTRY LINKED TO LUXEMBOURG , DURING THE PERIOD IN QUESTION , BY AN INTERNATIONAL CONVENTION ON SOCIAL SECURITY . THOSE WORKERS REMAINED COMPULSORILY AFFILIATED TO THE FRENCH SOCIAL SECURITY SCHEME DURING THE ENTIRE DURATION OF THE WORK CARRIED OUT IN LUXEMBOURG .
3 BY VIRTUE OF THE PROVISIONS OF THE LUXEMBOURG CODE DES ASSURANCES SOCIALES ( SOCIAL INSURANCE CODE ) WORKERS EMPLOYED IN LUXEMBOURG ARE IN PRINCIPLE COMPULSORILY INSURED UNDER THE OLD-AGE AND INVALIDITY INSURANCE SCHEME . HALF OF THE CONTRIBUTIONS MUST BE PAID BY THE EMPLOYER AND HALF BY THE WORKER . HOWEVER , BY VIRTUE OF THE SECOND PARAGRAPH OF ARTICLE 174 OF THAT CODE THE LUXEMBOURG GOVERNMENT MAY EXEMPT FROM INSURANCE FOREIGNERS WHO ARE ONLY TEMPORARILY RESIDENT IN THE GRAND DUCHY . IN THAT CASE , BY VIRTUE OF THE THIRD PARAGRAPH OF ARTICLE 174 OF THE CODE , THE EMPLOYER IS NEVERTHELESS LIABLE FOR THE SHARE OF CONTRIBUTIONS FOR WHICH HE IS PERSONALLY RESPONSIBLE , ALTHOUGH THOSE CONTRIBUTIONS DO NOT ENTITLE THE WORKERS CONCERNED TO ANY SOCIAL SECURITY BENEFIT .
4 IT APPEARS FROM THE PAPERS PLACED BEFORE THE COURT THAT THE REASON FOR THE ENACTMENT OF THE PROVISIONS CITED ABOVE WAS , ON THE ONE HAND , THAT IT WOULD BE UNFAIR TO COLLECT CONTRIBUTIONS FROM WORKERS RESIDING IN LUXEMBOURG ONLY TEMPORARILY , WHILST , ON THE OTHER HAND , THE TEMPTATION FOR EMPLOYERS TO USE FOREIGN LABOUR IN ORDER TO ALLEVIATE THE BURDEN OF PAYING THEIR SHARE OF SOCIAL SECURITY CONTRIBUTIONS MUST BE AVOIDED . NEVERTHELESS , IN PRACTICE THE EMPLOYER ' S SHARE OF CONTRIBUTIONS IS NO LONGER REQUIRED TO BE PAID BY EMPLOYERS IN RESPECT OF WORKERS WHO ARE TEMPORARILY RESIDENT IN LUXEMBOURG IF THEY ARE NATIONALS OF A MEMBER STATE OR PERSONS TREATED AS SUCH .
5 IN THIS CASE THE UNDERTAKINGS SECO AND DESQUENNE & GIRAL OBTAINED AN EXEMPTION FROM THE EMPLOYEE ' S SHARE OF INSURANCE CONTRIBUTIONS PURSUANT TO THE SECOND PARAGRAPH OF ARTICLE 174 OF THE CODE DES ASSURANCES SOCIALES BUT WERE HELD LIABLE BY THE LUXEMBOURG INSTITUTION FOR THE EMPLOYER ' S SHARE OF THOSE CONTRIBUTIONS PURSUANT TO THE THIRD PARAGRAPH OF THAT ARTICLE . THE TWO UNDERTAKINGS APPEALED AGAINST THAT DECISION , CLAIMING THAT THE LUXEMBOURG LEGISLATION IN QUESTION WAS NOT APPLICABLE TO THEM BECAUSE IT WAS DISCRIMINATORY AND LIKELY TO IMPEDE THE FREEDOM TO PROVIDE SERVICES WITHIN THE COMMUNITY .
6 THE COUR DE CASSATION OF THE GRAND DUCHY OF LUXEMBOURG CONSIDERED THAT ITS DECISION TURNED ON