Of the nine factions in parliament, eight have opposed changing the system, which they say would be regressive and undemocratic.
"The possibility of an election delay is high if the ruling is a closed system," said Bivitri Susanti of Indonesia's Jentera school of law, adding the election commission would need time to implement the necessary changes.
Fajar Laksono, the court spokesperson, confirmed a decision on the voting system was expected on Thursday.
The court case and talk of an election delay has added fuel to persistent speculation that allies of Jokowi want him to stay in power longer, a scenario he has officially rejected.
A higher court overruled that and Supreme Court has accepted the party's appeal.
Persons:
Fajar Laksono, Joko Widodo, Jokowi, Jokowi's, Ananda Teresia, Stanley Widianto, Kate Lamb, Martin Petty
Organizations:
Democratic Party of Struggle Party, Thomson
Locations:
JAKARTA