In 2005, a public hearing was held on the results of the Environmental Impact Assessment (EIA) for a 220-kV high-voltage line designed by REN that was to connect the Alto Mira substation in Amadora to the Trajouce substation in the municipality of Cascais; to do so, it would cross the municipality of Sintra. Sintra would be affected the most by the plan, as 27 of the 30 electricity towers were to be built there; in some cases, the towers would be installed only 25 meters from residential areas. It was only on the last day of the public consultation and thanks to the mobilization efforts of the Olho Vivo environmental organization that the local residents became aware of the project. The local civic movement criticized the lack of public participation in the consultation and demanded that the line be buried underground. The movement started a petition and collected more than 5,000 signatures. In 2006, in its environmental impact statement on the project, the Secretary of the Environment argued against placing the towers in the Alto Colaride archaeological site.

In August, Quercus and Olho Vivo announced it would launch legal proceedings against the Portuguese state for its failure to comply with the recommendations of the EIA report on the high-voltage line and for not conducting alternative studies, as required by European legislation. In March 2007, 100 people protested in Sintra. A parliamentary commission unanimously approved a public petition and announced that a working group composed of representatives from all parties would be created to follow up on the issue. The operation of the transmission line was temporarily suspended, but restarted shortly after. In December, an agreement was signed between REN and the Sintra City Council to bury part of the line. With the support of local authorities, this began to be done in March 2008.

Parallel to this, similar conflicts were occurring in other places in the country. In April 2007, a meeting of several civic movements opposing power lines was held. In August of that year, plans to install a high voltage line between Tunes and Estoi were improved, which would go through the municipalities of Silves, Albufeira, Loulé, and São Brás de Alportel. The neighborhood association of Vale Fuzeiros (Silves) began to actively question the installation of this line and the route chosen, and demand that the lines be displaced to the north as an alternative solution.

The Vale Fuzeiros association also presented a detailed report, in which it argued that the proposed route was very close to housing and would therefore affect ecological areas, organic farms, and tourism projects, and endanger local archaeological heritage. Despite the REN’s announcement that the route would be changed to safeguard existing archaeological remains in Vale Fuzeiros, the population did not accept this concession. In October, a vigil and hunger strike was organized near the São Bento Palace in Lisbon by the National Movement Against High Voltage Power Lines upon the initiative of the residents of Sintra and Silves. Further studies were carried out and new routes were proposed, but the population continued to protest and REN halted the construction of the Tunes-Estoi line in the valley. The Silves population celebrated this "desistence", but part of the line already built in Tunes-Estoi caused problems in other lines, such as in Alcalar and Poio, connecting the wind power of Espinhaço de Cão (Lagos) and Porto de Lagos (Portimão), and in the section of Albufeira substation. Under the pressure of mass protests, the Silves city council and Energias de Portugal (EDP) signed an agreement to run the high-voltage power lines underground.      Another project, the Foz Tua-Amamar high-voltage power line, crosses an area in the Alto Douro Vinhateiro region that has been classified by UNESCO as a world heritage site. In April 2012, in its environmental impact assessment, the Ministry of Environment stated its disapproval of the installment of the line because of the significant socioeconomic impacts it would have on land use, landscape, and the conservation of the cultural heritage of humanity. In a joint press statement, environmental organizations LPN, GEOTA, FAPAS and Associação Amigos do Vale do Rio Tua expressed their support for the Ministry of Environment's decision, emphasizing the Foz Tua dam project’s poor design. EDP announced that it would explore alternatives such as the need to bury the line, which the associations have described as an attempt to camouflage its negative impacts. The Platform Save Tua (founded by nine environmentalist organizations and a wine farm from the region in May 2013) challenged both the Foz Tua dam and the power line. The plans to build a hydroelectric dam and a high voltage line were approved and the works were completed in 2016.

In October 2016, the Assembly of the Republic approved regulations for the law that provides protection from the effects of high voltage lines, which defines several measures and requirements for this type of project.

In June 2017, the government announced its intention to advance the process of regulating the construction of more high voltage transmission lines as quickly as possible, which will create several restrictions on plans for the future.

The high-voltage line Tunes-Estoi has over 40 km and runs at 150 Kv.

In the project, the high-power line Foz Tua-Amamar has over 40 km and runs at 400 kV.