Operation Black Vote has released what it calls a "hard-hitting" poster urging black and ethnic minority voters to take part in the EU referendum.
It features "an elderly Asian British woman being berated by an aggressive thug", according to Operation Black Vote's description.
The campaign says it is meant to show everyone has the same voting power.
But UKIP leader Nigel Farage described it as a "disgusting" example of "sectarian politics".
And he accused Operation Black Vote, who he said he had previously supported, of "trying to divide society". "I want to engage people in all communities to get involved in our democracy but I'm afraid this poster is a really big mistake," he said.
Magnus Djaba, chief executive of Saatchi and Saatchi London, the ad agency which created the poster, said: "This is a message about democracy, not a message about race. Whichever community you're from, it hits home."
Operation Black Vote is running a series of voter registration events around the country in the run up to 23 June's referendum on whether Britain should remain in the EU.
Operation Black Vote director Director Simon Woolley said: "Perhaps the greatest thing about democracy is that one person's vote has no more value than another person's: A vote is a vote.
"With some Black and minority ethnic communities still unlikely to be registered to vote, we need to show them that their voices matter. These potential voters could easily decide one of the biggest questions of the last three decades - whether we remain in the EU or leave."
Operation Black Vote says there are about four million Black and Minority Ethnic voters and a further 400,000 citizens of Commonwealth countries entitled to take part in the referendum - but about 30% are not registered to vote, it says.