Parties in Ethiopia’s most populous region, Oromia, said they would boycott the election.
The Oromo Liberation Front (OLF) pulled out in March, citing the jailing of some of its leaders and the alleged closure of its offices by the government – including its head office in the capital.
It is one of the oldest parties in Ethiopia with a huge following in Oromia, where Prime Minister Abiy Ahmed comes from.
The Oromo Federalist Congress (OFC), the party of Jawar Mohammed, also announced in March that it was “forced” to pull out of the election on similar grounds.
It said those in prison include potential candidates, such as Mr Jawar, as well as its organisers and election observers.