Mexico's electoral authority has fined the party of President-elect Andrés Manuel López Obrador $10m (£7.7m) for breaking campaign finance laws.
The National Electoral Institute (INE) imposed the fine on the Morena party over a trust it had created for victims of September's devastating earthquake.
INE said it had found "profound irregularities" in the way the trust was set up and the money handled.
Morena said it would appeal against the fine, the highest imposed on any party.
The party won a majority in Mexico's Congress and its candidate, Mr López Obrador, widely known by his initials as Amlo, won the presidency in the general election on 1 July.
Morena and Amlo swept to power on a promise to battle Mexico's high levels of corruption
Morena formed the trust, called Por los demás (For the others), after more than 350 people were killed in a 7.1-magnitude earthquake which hit south of the city of Puebla last year.
But according to INE, the party did not report forming the trust and did not declare where the money taken out of the trust went.
The fund raised 78.8m pesos ( $4.1m; £3.2m), INE says.
The investigation came after a rival party, the Institutional Revolutionary Party (PRI) accused Morena of using the trust to channel public funds to its electoral campaign.
INE dismissed that accusation but found that the fund was "opaque" and broke electoral rules which ban parties from giving money directly to members of the public.
INE member Ciro Murayama said that "it's not an isolated case of irregular conduct but a scheme of parallel finance where a trust is created, which is allowed, but the authorities are not informed...
"The aim of the trust - to give the population money - is illegal for a party".
Morena's main rivals, the PRI and the National Action Party (PAN), were also fined, although their fines were not as high.
PRI for funnelling state money earmarked for workers' salaries into their campaign fund and PAN for accepting funds from private companies, which is not allowed under electoral laws in Mexico.