It also kicked out Mluleki George, who served as Lekota’s deputy during his tenure as defence minister.
A party statement issued before 7pm read: "The ANC national working committee (NWC) meeting in Bloemfontein today (13 October 2008), has decided to summarily suspend the ANC membership of Mosiuoa Lekota and Mluleki George with immediate effect."
The committee said this was in line with Rule 25.12 of the ANC constitution. This rule authorises the NWC to summarily suspend any member, pending the institution and conclusion of disciplinary proceedings against them.
"The NWC has agreed to convene a special meeting of the ANC National Executive Committee (NEC) this Wednesday where the matter will receive further attention," the statement read.
"The ANC will take similar action against any other members who have indicated in words or action their intention to establish a party in opposition to the ANC."
Lekota could not immediately be reached for comment.
The NWC said it would recommend to the NEC that provincial structures be directed to take disciplinary action against such individuals.
"The NWC believes that this action will address any confusion that may have been created by people speaking for the ANC at meetings not arranged or sanctioned by the ANC," the statement read.
Lekota last week announced his intention to hold a convention to discuss the possibility of forming a new political party.
He recently resigned as defence minister after the ANC leadership ousted Thabo Mbeki as president of the country.
In Monday’s statement, the NWC said the ANC could not allow its structures to be used "for purposes of undermining and betraying the organisation".
"While the ANC respects the right of any South African to form a political party, the NWC reiterates the fundamental principle that all ANC members have voluntarily undertaken to respect its decisions, internal processes and democratically-elected structures."
Grievances or concerns did not give any member a licence to defy decisions of ANC structures, to destabilise the organisation, or to engage in factional activity, the NWC said.
Lekota met ANC treasurer-general Mathews Phosa on Monday morning to discuss his concerns over the party.
Afterwards, Lekota told the SABC the meeting was not helpful.
"It was a very badly prepared-for meeting," he said.
"Although they said they were mandated by the national working committee [of the ANC], there was no record of the decision of the committee as to what their answers are to the questions I have raised.
"There is nothing you could put your finger on and say this is what the position of the ANC is."
Lekota held a rally in Langa, Cape Town, to drum up support for the idea of a national convention.
In the Free State, a group of disgruntled ANC members announced on Monday that a provincial convention would be held to test support for a national convention.
There were also indications of support for the idea in the Eastern Cape, The Herald Online reported on Monday. According to the report Lekota was scheduled to hold three meetings in Nelson Mandela Bay on Monday afternoon.
He was to address business and church leaders at the Edward Hotel in Port Elizabeth at 1pm. Then he was to speak at a rally in the Babs Madlikane Hall in Uitenhage at 4.30pm, winding up the visit with another speech at the Nongoza Jebe Hall at 6.30pm.
Mluleki George was reportedly also expected to speak in Port Elizabeth on Monday.
Those expected to attend included former head of the ANC presidency Smuts Ngonyama and some business leaders.
ANC secretary general Gwede Mantashe spent the weekend in the Eastern Cape addressing a provincial alliance summit in King William’s Town, and the Cacadu regional council in Humansdorp.
Party spokesperson Andile Nkuhlu told the Herald that Mantashe had urged members not to leave the ANC. – Sapa