Article 25 of the International Covenant on Civil and Political Rights (adopted by the UN in 1966) provides that

Every citizen shall have the right and the opportunity, without any of the distinctions mentioned in article 2 and without unreasonable restrictions:
(a) To take part in the conduct of public affairs, directly or through freely chosen representatives;
(b) To vote and to be elected at genuine periodic elections which shall be by universal and equal suffrage and shall be held by secret ballot, guaranteeing the free expression of the will of the electors;
(c) To have access, on general terms of equality, to public service in his country.