According to the TVE broadcaster, they will be asked whether they knew or not about the existence of a "b-box," or an unofficial party fund that was topped up through illegal means, an allegation put forward against the entire party leadership by former treasurer Jose Luis Barcenas, now jailed for 33 years within the same case.
The large-scale scandal involving the PP's illicit funds has been ongoing for several years now and is known in Spain as the Gurtel case. It alleges businessman Francisco Correa Sanchez in using the party and its members for money laundering and tax evasion at the cost of bribes and kickbacks.
The upcoming trial is specifically about 900,000 euros ($980,000) that the party spent for its Madrid headquarters' renovation in 2007-2008 – the prosecution believes the money came from the unaccounted shadow fund.
This will be Rajoy's second time to testify within the Gurtel case. In 2018, it cost him a vote of no confidence and subsequent ouster as prime minister.