With Islamist parties including the Muslim Brotherhood's Freedom and Justice Party planning nationwide campaigns, boycotts by liberals and leftists will enhance the chances of the Islamists securing a commanding say in the new parliament.
The Popular Current, led by former presidential candidate Hamdeen Sabahy, also planned to boycott talks called by President Mohamed Mursi later on Tuesday to discuss guarantees for ensuring a free and fair vote, said Heba Yassin, a spokeswoman for the party.
"We will neither participate in the national dialogue nor in the elections," she told Reuters. Sabahy came in a close third in Egypt's first free presidential election last year.
The hardline Salafist Nour Party, the second biggest Islamist group, announced on Monday that it planned to take part.
The Dustour Party, a liberal group headed by Mohamed ElBaradei, has also decided to boycott the vote, to be held in four stages starting in late April.
Yassin of the Popular Current added: "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."
(Writing by Tom Perry and Shaimaa Fayed; Editing by Kevin Liffey)