Egyptian leftist opposition party the Popular Current, led by former presidential candidate Hamdeen Sabahi, said it will boycott parliamentary elections due to start in April.
It also plans to boycott national dialogue talks proposed by President Mohammed Mursi.
"We will neither participate in the national dialogue nor in the elections," Heba Yassin, a spokesman for the party said.
"This is to protest against the elections law that we did not participate in drafting, and about which our opinion was not taken.
"Also we reject the continuation of Mursi's oppressive policies that have led to nothing but more bloodshed and political problems."
Mr Sabahi came in a close third in the country's first free presidential elections, which took place last year.