A KBA or agreement between the company and workers` representatives may introduce an irregular distribution of working time throughout the year (i.e. an annual agreement on working time). In the absence of an agreement, the company can allocate only 10% of irregular working time throughout the year, with the rest set. Distribution must be consistent with the minimum legal periods of rest and weekly rest and workers must be informed five days before the exact date and time of irregular working days. There are no official national figures on tariff security. The way collective agreements are generally calculated takes into account the average number of persons affiliated with social security in a given year, divided by the total number of people whose working conditions are governed by a collective agreement. Based on 2016 data, the last year for which final figures on collective agreements are available, and statistics on social security membership in the general scheme (i.e. excluding the self-employed and special social security schemes such as domestic workers), a coverage rate of 81.6% is obtained. However, this estimate poses some methodological problems that mainly concern the problems of statistics of collective agreements. The structure of collective bargaining has remained fairly constant since the late 1990s. The structure of collective agreements in most Spanish sectors is characterized by its multi-level character, with collective agreements signed at the national, sectoral, provincial and/or professional level. Since 2002 (with the exception of 2009), state-of-the-art inter-professional agreements have set only guidelines for working time and remuneration that are not legally binding. In terms of the number of agreements covered by economic activity, the overweight of enterprise agreements prevails.
The two largest are provincial sectoral agreements, followed by national and regional sectoral agreements. On the other hand, most workers are covered by provincial sectoral agreements and national sector agreements. Attempts to create a more coherent structure to date, including a 1997 reform agreement by employers and trade unions, have not been successful. However, in the wake of the financial and economic crisis, a new model could emerge. In 2011, the Socialist government introduced legislative changes (RDL 7/2011) that gave a greater role to enterprise negotiations, and the current centre-right government continued to move in the same direction in 2012 with additional laws (Ley 3/2012) – developments that trade unions rejected.