refer to the decision adopted by the Human Rights Committee on 9 April 1987 in communication No. 172/1984, which states, inter alia, that article 26 of the Covenant is not limited to the civil and political rights provided for in the Covenant but also applies to social insurance law. Concerning the differences noted above in the treatment of owners of physiotherapy practices, the authors allege that it is possible to speak of a violation of article 26 in conjunction with article 14, paragraph 1, of the Covenant. They contend that the distinction made by BVG in practice is an arbitrary one. 3. By decision dated 15 March 1988, the Working Group of the Human Rights Committee transmitted the communication to the State party under rule 91 of the Committee s provisional rules of procedure, requesting information and observations relevant to the question of the admissibility of the communication. By note dated 6 July 1988, the State party requested an extension of three months for the submission of its observations. 4.1 In its submission under rule 91, dated 28 October 1988, the State party objects to the admissibility of the communication on a number of grounds. Recapitulating the facts, it points out that the alleged victims are joint owners of a physiotherapy practice where a part-time physiotherapist worked on the basis of a co-operation contract as from 1982; she was paid by invoice, worked more or less independently and was not insured as an employee under social security legislation. The State party further indicated that there are three social security insurance schemes: schemes paid out of public funds, national insurance schemes and employee insurance schemes. Unlike the first two, employee insurance schemes are only applicable where there is an employer/employee relationship. Both employer and employee pay part of the employment insurance contribution, determined in accordance with a standard formula. This contribution is calculated as a certain percentage of the employees income and is payable to the competent industrial insurance board. 4.2 The State party explains that for the purpose of determining who, as an employee, should pay employment insurance contributions, a broad definition of the term employment is used. It is not confined to situations in which there is an employment contract governed by civil law but also extends to co-operative relationships that meet certain criteria defined by the relevant act of parliament or the executive rules and regulations based on it; in accordance with these criteria, employment relationships not governed by employment contracts can be equated with those that entail, with all the relevant consequences concerning entitlement to benefits, an obligation to pay contributions. 4.3 In the past it had been generally assumed that a physiotherapist working for a physiotherapy practice who was paid by invoice should not normally be regarded as being employed by the practice. However, the Central Appeals Board took a different view in its judgement of 19 April 1983. BVG is entrusted with the implementation of social security legislation with regard to employees in the health sector and must determine the social insurance contributions of employers and employees for employee insurance schemes such as medical insurance, disability insurance and unem-ployment insurance contributions. As from 1 January 1984, BVG claimed these contributions from the applicants for the aforementioned physiotherapist. The applicants did not agree that this date was correct and contested the decision on the grounds, inter alia, that the principle of equality had been violated because other physiotherapists had only been required to pay contributions as from 1986. The Court of First Instance, the Board of Appeals and the Court of Second and Last Instance, the Central Appeals Board dismissed the case. The main reason for the dismissal of the case was that peremptory statutory provisions had been properly applied, that such provisions must always be applied unless there are special circumstances, and that these were lacking in the author s case. 4.4 With respect to the requirement of exhaustion of domestic remedies, the State party acknowledges that the authors pursed legal proceedings up to the Court of Last Instance. It points out, however, that the authors did not invoke either article 26 or article 14, paragraph 1, before the Board of Appeal and, on appeal, before the Central Appeals Board. It was merely in a supplementary petition to the Central Appeals Board, dated 29 April 1987, that the principle of equality was also mentioned, if only in general terms and without specific reference to provisions of domestic or international law. Nor were the articles of the Covenant invoked by the authors in either of the judgements given in the case. In these circumstances, the State party does not consider it to be altogether clear that the applicants have exhausted domestic remedies, as they did not explicitly invoke any provisions of the Covenant during domestic proceedings . The State party requests the Committee to decide on whether and to what extent 65