Puerto Rico Constitution
Article III - The Legislature
Section 7.

Section 7. If in a general election more than two-thirds of the members of either house are elected from one political party or from a single ticket, as both are defined by law, the number of members shall be increased in the following cases:

(a) If the party or ticket which elected more than two-thirds of the members of either or both houses shall have obtained less than two-thirds of the total number of votes cast for the office of Governor, the number of members of the Senate or of the House of Representatives or of both bodies, whichever may be the case, shall be increased by declaring elected a sufficient number of candidates of the minority party or parties to bring the total number of members of the minority party or parties to nine in the Senate and to seventeen in the House of Representatives. When there is more than one minority party, said additional members shall be declared elected from among the candidates of each minority party in the proportion that the number of votes cast for the candidate of each of said parties for the office of Governor bears to the total number of votes cast for the candidates of all the minority parties for the office of Governor.

When one or more minority parties shall have obtained representation in a proportion equal to or greater than the proportion of votes received by their respective candidates for Governor, such party or parties shall not be entitled to additional members until the representation established for each of the other minority parties under these provisions shall have been completed.

(b) If the party or ticket which elected more than two-thirds of the members of either or both houses shall have obtained more than two-thirds of the total number of votes cast for the office of Governor, and one or more minority parties shall not have elected the number of members in the Senate or in the House of Representatives or in both houses, whichever may be the case, which corresponds to the proportion of votes cast by each of them for the office of Governor, such additional number of their candidates shall be declared elected as is necessary in order to complete said proportion as nearly as possible, but the number of Senators of all the minority parties shall never, under this provision, be more than nine or that of Representatives more than seventeen.

In order to select additional members of the Legislative Assembly from a minority party in accordance with these provisions, its candidates at large who have not been elected shall be the first to be declared elected in the order of the votes that they have obtained, and thereafter its district candidates who; not having been elected, have obtained in their respective districts the highest proportion of the total number of votes cast as compared to the proportion of votes cast in favor of other candidates of the same party not elected to an equal office in the other districts.

The additional Senators and Representatives whose election is declared under this section shall be considered for all purposes as Senators at Large or Representatives at Large.

The measures necessary to implement these guarantees, the method of adjudicating fractions that may result from the application of the rules contained in this section, and the minimum number of votes that a minority party must cast in favor of its candidate for Governor in order to have the right to the representation provided herein shall be determined by the Legislative Assembly.