Adam Andruszkiewicz has been called to appear before prosecutors on 11 February over allegations that signatures were forged to support candidates from the far-right All-Polish Youth movement in 2014 local elections.
Andruszkiewicz led the nationalist organisation at the time.
President Nawrocki criticised the investigation on Thursday, calling it a politically motivated attack.
"Twelve years of investigation without evidence," he wrote on social media, questioning why prosecutors were acting now despite what he said were expert opinions clearing his aide.
Andruszkiewicz, a politician from the Law and Justice party (PiS) who was previously associated with the far-right All-Polish Youth (Młodzież Wszechpolsk) and National Movement (Ruch Narodowy), has dismissed the move as "political revenge" and part of a broader campaign against the presidential office by the current government.
The investigation was initially handled by prosecutors in Białystok but was transferred to Lublin in 2019 due to concerns about how the case was being conducted.
Prosecutors there expanded the probe, appointing handwriting experts and interviewing hundreds of witnesses.
President Nawrocki appointed Andruszkiewicz as deputy head of the presidential chancellery in August last year.
(ał)
Source: PAP