DLA Piper has been the focus of protests in Washington DC over its role advising the Ethiopian government.
Adverts have been posted on a taxi bearing the slogan “DLA Piper shares blood money with Ethiopian dictators”, according to legal website Above The Law.
The firm acted for the country’s prime minister Meles Zenawi last year, lobbying Congress not to sanction the country over alleged human rights abuses.
The Ethiopian government carried out a violent crackdown on protests after elections in 2005, according to human rights observers.
The US is threatening to withdraw military and place other sanctions on the country. DLA Piper partners Dick Armey and Gary Klein campaigned against the bill on behalf of Zenawi.
The firm, which has a growing presence in Africa, said it was no longer acting for the Ethiopian government but defended its involvement with what it said was “an important ally” of the US.
A statement said: “There are some very vocal elements of the Ethiopian diaspora, particularly in the Washington area, who are opponents of the current administration in Ethiopia and go to great lengths to try to embarrass or demean those who are associated with it.
“While we disagree with these individuals and don’t believe their views reflect the majority of Ethiopian Americans, we fully support their right to voice their opinions on this matter.”
DLA Piper has associate offices in South Africa (DLA Cliffe Dekker Hofmeyr) as well as in Egypt, Ghana, Tanzania and Zambia.