MADRID (AP) — Months of simmering tensions within Spain's main opposition party came to a head on Friday amid fresh revelations that Popular Party members tried to launch an alleged smear campaign against a rising star from the party's ranks.

Members of the conservative party allegedly tried to hire detectives to investigate a facemask-supplying contract brokered during the worst of the coronavirus pandemic by a relative of Madrid's regional president, Isabel Díaz Ayuso.

Díaz Ayuso, whose meteoric political rise has threatened to overshadow Popular Party leader Pablo Casado, has acknowledged that her brother benefitted from the contract. But she denied any wrongdoing and painted the investigation as a political vendetta.

The scandal comes as the Popular Party is struggling to hold back the rise of a far-right party founded by some of its former members. The party, Vox, has become the third political force in the country's fragmented national parliament.

Vox made significant strides in last week's snap election in the Castilla y León region of northwestern Spain. Regional Popular Party authorities had hoped to repeat Díaz Ayuso's success in a Madrid vote last year and allow it to form a regional government on its own.

The Popular Party came first in Castilla y León, but failed to gain a majority of regional assembly seats. The party is now weighing its options to hold on to power including seeking out help from historical rivals, the center-left Socialists who lead the national ruling coalition. The move could be perceived as weakness, but the alternative of a partnership with Vox would embolden the far-right and open the party to criticism both domestically and in Europe.

Ayuso and Casado were former friends who rose to top positions at the end of 2018 when the party tried to make a fresh start following a wave of corruption scandals that cost the conservatives the nation's leadership.

But their relationship eroded as Casado tried to battle the national left-to-center coalition and Ayuso emerged as an ardent critic of Prime Minister Pedro Sánchez and his administration's handling of the pandemic.