With regards to the autonomous communities, the Senate plays a more important role than Congress. As the house of territorial representation, the Senate actually plays a double role. On the one hand it exercises a certain amount of control over the communities as part of the central power, while on the other hand it also represents the communities in the national decision making process. As such, the Senate has the important exclusive right of deciding whether or not an autonomous community has failed to comply with its constitutional and other juridical obligations or is conflicting with the public interest if such would be claimed by the government. Whether or not it is in the public interest to harmonise the concerned legislation is left to the executive and parliament to decide. However, the constitutional court restricted this authority in various rulings, determining that an appeal to the public interest may only be made if there is an urgent necessity for state interference.As such, the public interest does not allow the central government to assume or infringe on competencies that explicitly belong to the autonomous communities, except in certain special circumstances mentioned in the constitution (art.155SC and150.3SC). The government must furthermore prove that these infringements are urgently necessary. With regards to the duration and form, the measures issued by the state must furthermore be in accordance with this necessity.
Both houses must furthermore parallel approve agreements of co-operation between the autonomous communities (art.145.2SC). This is also the case for the allocation of national resources to the autonomous communities through the Inter-regional Allocation Fund (art.158.2SC). If the houses do not agree, a joint committee of both senators and deputies must seek an agreement which again needs the approval of both houses, though this time by a simple majority. If an agreement on either the allocation of a fund, or an inter-regional agreement of co-operation would again fail to obtain the required majority of both houses, the whole issue will be placed in the hands of Congress. The latter must then solely decide on the issue by an absolute majority.
Both houses are also responsible to draw up or approve laws to harmonise the legislation of the autonomous communities by absolute majority, if such is required by the public interest (art.150.3SC).
As opposed to the previous restrictive powers, parliament also has exclusive competencies the enhance the scope of the autonomous communities through article 150.1SC. Latter article allows the Cortes Generales to attribute competencies to one or more community through framework laws. These laws have the rank of ordinary laws and outline the objectives and principles of the matters to be transferred or delegated to the autonomous communities. Though the communities obtain full responsibility for these matters and also the right to enact territorial laws, parliament can still enact its own laws with regards to these matters. As such, parliamental laws regarding these matters have precedence over territorial laws.
As stated previously, a special committee is currently investigating how to transform the Senate into a genuinely territorial chamber. As such, the autonomous communities will not only have much more say in state affairs, but it will aversely affect the parliamentary powers regarding the communities. This will surely have an impact on the role of parliament and more then likely will increase the importance of the Senate. Especially since the autonomous communities are getting more and more financial and political significance.