South African police were investigating Tuesday if former President Jacob Zuma’s new political party forged supporters’ signatures to register for national elections next month.

The MK Party, which has been highly critical of the ruling African National Congress he used to lead, has been embroiled in legal cases over whether it and Zuma are eligible to contest the May 29 national and provincial elections. They could be the most pivotal in South Africa in the last 30 years.

The MK Party had its registration last year rejected by the Independent Electoral Commission before a second attempt was successful. Zuma was ruled ineligible to stand as a candidate for Parliament because of his criminal conviction for contempt of court and prison sentence in 2021, but an appeal was successful and a final Constitutional Court ruling comes next month.

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The new investigation into the MK Party came after a national newspaper reported Sunday that a former party official has told police there was an elaborate scheme to forge some of the 15,000 signatures required for parties to register for the elections.

The Independent Electoral Commission called for an investigation, and National Police Commissioner Gen. Fannie Masemola said Tuesday that an inquiry had been opened in Cape Town, where the forgery allegedly occurred. Masemola said the investigation would establish if there was a case for prosecutors.

Zuma rocked South African politics when he announced in December that he was joining the MK Party as its de facto leader and would be campaigning against the ANC, which he led from 2007-2017. Zuma was president of South Africa from 2009-2018 but was forced to step down by the ANC amid corruption allegations.

Zuma is accused of overseeing a period of rampant graft by some senior ANC and government officials in Africa’s most developed economy. He is currently on trial for corruption, although that case has been held up for three years by legal delays.

Since his resignation, he has been fiercely critical of President Cyril Ramaphosa, his successor as head of the country and the ANC.

Next month’s election could be the most important since the ANC came to power at the end of the apartheid system of racial segregation in 1994. Numerous polls and analysts predict that the ANC could lose its parliamentary majority for the first time amid growing discontent and be forced into a coalition to stay in government.

Despite his legal troubles, Zuma remains popular in some parts of South Africa and his new MK Party is expected to take some of the ANC’s vote if it’s allowed to stand after the new allegations against it.

The MK Party is likely to be disqualified from the elections if it is found to have forged signatures.