Income gaps by level of education reflect monetary incentives that offer someone to invest in education. Post-education income gaps are the intersection of supply and demand curves for educated workers. The relative income differences between countries reflect a number of factors. B the demand for skills in the labour market, minimum wage legislation, the strength of trade unions, collective agreements, the supply of workers with different levels of education, the work experience of workers with a high and low level of training, the distribution of employment between occupations and the relative impact of part-time and seasonal work (OECD) , 2007). If we compare Table 4.2 to Table 4.1, we can get an approximate overview of the changes that have taken place since 1990. In the public sector, there appears to have been a significant shift of jobs and workers to registered collective agreements. In the private sector, the changes appear to be less dramatic and more fragmented. Rewards remain important, particularly in sectors such as hotels and restaurants and retail, where large numbers of women work, often underpaid. While there is a shift in distinctions in the private sector, it is both the move towards the less regulated sector of unregistered individual contracts and the transformation into registered collective agreements. An extremely important aspect is the limitation of the effectiveness of collective agreements in relation to the individual employment contract. Under Article 14, paragraph 1, employment contracts can always improve the terms set by the agreements, which means that they can never be considered absolutely binding standards for individual contracts. Individual autonomy can always improve the system of collective autonomy in favour of the worker. In the United States, the National Labor Relations Act (1935) covers most collective agreements in the private sector.
The Act makes it illegal for employers to discriminate, spy, harass or terminate workers because of their union membership or to retaliate for organizing campaigns or other “concerted activities,” creating business unions or refusing to engage in collective bargaining with the union that represents their employees. It is also illegal to require any worker to join a union as a condition of employment.  Trade unions are also able to ensure safe working conditions and adequate remuneration for their work. Disability both employers and employees, whether individually or represented by trade unions and employers` organizations, have the right to take action in labour courts to request all the clauses of collective labour regulatory agreements that they consider invalid (Article 43, Collective Work Act).