* "Vote No!" campaign appealing to disillusioned voters
* Ruling ANC party still expected to win May 7 poll
* President Jacob Zuma hit by several graft scandals
By Joe Brock
JOHANNESBURG, April 15 (Reuters) - Dissident veterans in South Africa's African National Congress (ANC) urged voters on Tuesday to spoil their ballots at a national election next month, in a protest against corruption intended as a wake-up call to the ruling party.
Former intelligence minister Ronnie Kasrils and ex-deputy health minister Nozizwe Madlala-Routledge said their "Sidikiwe! Vukani! (We've had enough! Wake up!) Vote No!" campaign was a warning shot at President Jacob Zuma and his ANC leadership.
"Our leaders need to see there are a growing number of disgruntled people in our country," Madlala-Routledge told reporters at the University of Witwatersrand in Johannesburg.
"We are calling on all South Africans to come out on the 7th May to use this democratic right for which people died ... use your right to express your feelings about our leaders."
The ANC, the former liberation movement in power in South Africa since the end of apartheid in 1994, has easily won every election since then. It is expected to secure victory again in the May 7 vote, though with a reduced majority that reflects its waning support in recent years.
The party won nearly two-thirds of the vote in the last elections, in 2009.
ANC leader Zuma is expected to be re-elected by parliament for a second five-year term as president after the election next month, even though several corruption scandals have blotted his reputation and turned many voters against him.
The "Vote No!" campaign promoted by Kasrils and Madlala-Routledge is seeking to tap into a growing group of ANC supporters who have little connection with opposition parties but feel the political leadership has become complacent.
"Right now, there is no one to vote for," said Nthato Moagi, a 22-year-old aeronautical engineering student. He said he would spoil his ballot at the election in three weeks. "The ANC is the party to lead us forward, but we need to wake them up from the comfortable slumber they are in."
The ANC has said the dissident "Vote No!" campaign is an insult to the work done by electoral authorities to strengthen democracy since the end of white-majority rule 20 years ago.
"It is treacherous that, after all that work and money spent, people want to encourage South Africans to go to the ballot box and spoil their votes. It is irresponsible, " Defence Minister Nosiviwe Mapisa-Nqakula said.
Zuma has been accused by the main opposition Democratic Alliance of running away from explaining his role in an anti-graft report, which slammed an "excessive" $23 million state-funded security upgrade to his home.
Political analysts believe if the ruling party gets a majority of less than 60 percent of the total vote, Zuma's opponents within the ANC may be emboldened to challenge his leadership, just as Zuma did when ousting former president Thabo Mbeki in 2007. (Editing by Pascal Fletcher and Larry King)