Each constituency was entitled to an initial minimum of two seats, with the remaining 39 allocated among the constituencies in proportion to their populations. The electoral law provided that parties, federations, coalitions and groupings of electors were allowed to present lists of candidates. However, groupings of electors were required to secure the signature of at least 1 percent of the electors registered in the constituency for which they sought election. Electors were barred from signing for more than one list of candidates. Concurrently, parties and federations intending to enter in coalition to take part jointly at an election were required to inform the relevant Electoral Commission within ten days of the election being called.
Election date
The term of the General Junta of the Principality of Asturias expired four years after the date of its previous election. The election Decree was required to be issued no later than the twenty-fifth day prior to the date of expiry of parliament and published on the following day in the Official Gazette of the Principality of Asturias, with election day taking place between the fifty-fourth and the sixtieth day from publication and set so as to make it coincide with elections to the regional assemblies of other autonomous communities. The previous election was held on 8 May 1983, which meant that the legislature's term would have expired on 8 May 1987. The election Decree was required to be published no later than 14 April 1987, with the election taking place no later than the sixtieth day from publication, setting the latest possible election date for the General Junta on Saturday, 13 June 1987. The General Junta could not be dissolved before the date of expiry of parliament except in the event of an investiture process failing to elect a regional President within a two-month period from the first ballot. In such a case, the General Junta was to be automatically dissolved and a snap election called, with elected deputies merely serving out what remained of their four-year terms.
Opinion polls
The table below lists voting intention estimates in reverse chronological order, showing the most recent first and using the dates when the survey fieldwork was done, as opposed to the date of publication. Where the fieldwork dates are unknown, the date of publication is given instead. The highest percentage figure in each polling survey is displayed with its background shaded in the leading party's colour. If a tie ensues, this is applied to the figures with the highest percentages. The "Lead" column on the right shows the percentage-point difference between the parties with the highest percentages in a given poll. When available, seat projections are also displayed below the voting estimates in a smaller font. 23 seats were required for an absolute majority in the General Junta of the Principality of Asturias.
