The marchers, who set out from Karachi on Sunday, reached the capital on Wednesday night, Dawn news reported.
"It is for the people to decide what our next strategy should be," Rehman aid in an exclusive interview with Aaj News.
Rehman, who is leading the March into the capital, said the chance of his party giving time to the PTI-led government has "ended".
He added that there would be "chaos" in the country if the PTI-led government refuses to resign in the aftermath of his Azadi March protest.
"We have to finally get the resignation from them (the government). And we will fight for it," the JUI-F supremo told Aaj News.
Hinting at a sit-in, he said his party wants to give the government a time period of two-three days "while sitting in Islamabad".
On Thursday morning, Pakistan Peoples Party (PPP) chairman Bilawal Bhutto Zardari visited the main camp of marchers and addressed them, saying all opposition parties have gathered at one platform to give a clear message to Prime Minister Imran Khan that the time has come for him to step down, Dawn news reported.
Calling Khan a "puppet", he said the nation was not ready to bow its head before a "selected" Prime Minister and "those who have selected him".
"We are not ready to bow before any selector or dictator... The hub of power is people and not the state."
Fazl had announced in June that his party had decided to hold an anti-government long march to Islamabad in the month of October in a bid to topple the government, which he sad had come to power through "fake" elections.
( With inputs from IANS )