The crackdown on the PML-N, whose leaders have accused the establishment of attempting to destabilize the party, comes a day before the party founder, ousted Prime Minister Nawaz Sharif, is due to return to Pakistan where he faces arrest. [She is] still not conscious and on ventilator.
He also criticised the court's decision to sentence his daughter to a seven-year term in jail, saying those who did so "did not even remember in their hate what stature daughters have in Pakistan".
"We received instructions to take prominent PML-N activists from their areas to avoid a law and order problem", the official told Reuters.
Nawaz and daughter Maryam left for Pakistan from London on late Thursday night.
Sharif and daughter Maryam landed at UAE's Abu Dhabi International Airport on Friday morning.
The caretaker government in Punjab has intensified the crackdown against PML-N ahead of the Sharifs' homecoming rally.
Hours before his imminent arrest, Mr Sharif said, "Maryam and I are coming back to face prison, and even if they send me to the gallows, we know that freedom can not be won without sacrifice. This opportunity will not come again", he said.
"Despite seeing the bars of prison in front of my eyes, I am going to Pakistan", he told a conference of his Pakistan Muslim League-Nawaz or PML-N party in London.
PML-N leaders claimed that around 300 workers were arrested from Rawalpindi on Tuesday, while several hundred others had been picked up from Lahore and other cities.
Recent opinion polls suggest PML-N has lost its lead nationally to the Pakistan Tehreek-e-Insaf (PTI) party of arch-rival Khan, whose anti-corruption message has resonated with many Pakistanis.
Their return could shake up an election race marred by claims Pakistan's powerful military was skewing the contest in favour of ex-cricket hero Imran Khan.
Muhammad Mehdi, the party's media coordinator, told Reuters that almost 500 workers had been detained in a "massive crackdown", including raids on the homes of a number of some of the party's local councillors.
Further, the PML-N president said the verdict in the Avenfield reference was "unjust".
Mr Sharif was sentenced by a court in Islamabad last week over the purchase of high-end properties in London.