Shops were closed on Saturday in parts of the nation's biggest city, Karachi, and in Peshawar, the capital of North West Frontier Province.
Business activity also slowed in Lahore, the capital of eastern Punjab province and Quetta, the capital of the south western province of Baluchistan, where police said men from the Islamic coalition damaged some shops and vehicles.
The six-party Mutahida Majlis-e-Amal, or United Action Forum, also called MMA, issued the call for a nationwide strike last month to reject President General Pervez Musharraf's policies and pressure him to resign.
On Friday, police arrested hundreds of MMA activists, including five lawmakers, in southern Sindh province of which Karachi is the capital.
Dozens of MMA supporters have
Karachi police chief Tariq Jamil said five lawmakers and 250 other people had been detained over the past 24 hours to maintain law and order.
Dozens more were detained on Saturday in Lahore after clashes with police.
Quetta police chief Salman Haider said there was some violence in Quetta.
Pakistan is a key ally of the United States in its "war on terror", but the MMA has opposed Musharraf since US-led forces attacked Afghanistan to oust the former Taliban government for sheltering Usama bin Ladin.
The MMA has been holding anti-Musharraf rallies since December, when the president reneged on a promise to resign from his position as army chief.
Last year, the MMA struck a deal with Musharraf, agreeing to accept him as president until 2007 in exchange for his promise to quit his army post before 31 December 2004.
Musharraf broke his promise of
standing down as army chief
The group has accused Musharraf of serving US interests instead of working to improve his people's lives. Musharraf, who seized power in a bloodless coup in 1999, was voted in for a five-year term as president in a 2002 referendum in which he was the only candidate. He later changed the constitution to enhance his powers, giving him the right to dismiss the prime minister, cabinet and parliament.