Islamic activists in Multan, in the Pakistani province of Punjab, have threatened to burn down posters featuring images of women if city officials do not remove them within two days.
North-West Frontier Province has seen the strongest protests
On Friday, the activists smeared three billboards put up by multinational companies in the city with black paint.
Also on Friday, North-West Frontier Province (NWFP) officials suspended three senior policemen for failing to act against activists who smashed billboards carrying photographs of women two weeks ago.
The incidents came four days after NWFP voted to introduce the hardline Islamic Sharia law.
'Contrary to Islamic law'
In Multan, the local leader of the Shabab-e-Milli religious group, Shehzada Babar, said daubing the billboards was "a token protest" to warn officials of further action.
Around 300 members of Shabab-e-Milli, the youth wing of the Jamaat-e-Islami group, took part in the protest at a busy intersection in the city, which lies 420km (262 miles) south of Islamabad.
Mr Babar said: "These multinational companies want to promote obscenity, lewdness and vulgarity by showing women in different poses.
"We will not let them do so."
He denied the group was vandalising private property.
"It is they who are acting contrary to Islamic law by
promoting vulgarity," Mr Babar said.
Recent similar acts against posters and billboards have taken place in Lahore and Peshawar.
No police action was taken in these incidents and companies stopped displaying women as a precaution.
Police in Peshawar have burned thousands of "un-Islamic" items
On Wednesday, Pakistani President Pervez Musharraf sacked the head of police and the chief civil servant in NWFP following concern that they had failed to maintain law and order in the provincial capital, Peshawar.
Islamabad officials cited cases of Islamic vigilantes attacking video shops and billboards in the name of eliminating obscenity.
On Friday, a superintendent, his deputy and an inspector in Peshawar were suspended for failing to stop Jamaat-e-Islami members destroying posters.
On Monday, NWFP voted to give Sharia precedence over secular provincial law.
Critics fear a re-run of life under the Taleban, the Islamic hardliners who ruled Afghanistan.
Supporters say it will curb obscenity and protect human decency.
Hardliners have been cracking down on activities they consider un-Islamic since an alliance of religious parties swept to power in North-West Frontier Province last October.