E/CN.4/2000/82 page 12 deny migrants certain advantages and also apply rules on job security that differ from those applied to nationals; sometimes they are excluded from the regulations on working conditions and denied the right to take part in trade union activities. The ILO Migrant Workers (Supplementary Provisions) Convention, 1975 (No. 143) deals, in its part I, with migrations in abusive conditions and, in its part II, with equality of opportunity and treatment. 52. The incorporation of this complex set of issues into international standards is one of the features of the International Convention on the Protection of the Rights of All Migrant Workers and Members of Their Families, which has been ratified by 12 countries. 53. As regards the children of migrants, there is resistance in some States to registering or enrolling the children of immigrants in school for fear that the general educational level will fall. In dealing with this issue, it should be remembered that those children have to adapt to different customs and languages, unless special measures are taken to help them overcome their difficulties. 54. In many countries, there are laws and practices that discriminate against foreigners seeking work in a country that is not their own. The granting of visas on the basis of the applicant’s country or continent of origin and labour market regulations based on discriminatory criteria, together with xenophobia in the name of national security, nationalism or national preferences, are some of the most common realities that migrant workers have to live with and that give the Special Rapporteur cause for concern. B. Violence against women migrant workers 55. The Special Rapporteur believes it is very important to tackle the problem of violence against women migrant workers as a vulnerable group. 56. Due to their double marginalization as women and as migrants, women migrant workers may easily find themselves in situations in which they are vulnerable to violence and abuse, both at home and at work (see E/CN.4/1998/74/Add.1). Women migrant workers dominate the informal labour market of most countries, working as domestic, industrial or agricultural labour or in the service sector. When women, most of whom are heads of household, find themselves in social circumstances that make it difficult for them to find paid work, they are forced to migrate. The way in which gender roles are traditionally established and the fact that men often do not share the domestic chores, particularly looking after children on a daily basis, make it even more difficult for women to develop personally and professionally. That situation often discourages women from staying in their families and/or places of origin. Migrant women, like many other women who do not migrate but who work outside the home, often leave their children in the care of family members or someone else. In many cases, particularly when the father is mostly or completely absent, this leads to the loss of sources of affection and to family breakdown. Both women who have been the victims of trafficking and those who migrate voluntarily may end up in situations of exploitation, violence and abuse, all of which have their origin in a situation like the one described above. The exchange of sexual favours for permission to transit, which is common practice on some frontiers, is also a form of gender-based harassment to which migrant women are often subjected.