Pakistani authorities issued a final warning on Friday to members of a party blocking a main road into the capital, raising fears of a violent clash.
Hundreds of supporters of the Tehreek-e-Labaik Pakistan party have been blocking the route into Islamabad for nearly 10 days, demanding the minister of law be sacked.
"You all are being given a last warning," the Islamabad deputy commissioner said in the order.
A court had already ordered the party to end the protest, the order added. "After this final announcement, you all are being warned to end the illegal sit-in immediately."
Tehreek-e-Labaik blames the minister, Zahid Hamid, for changes to an electoral oath that it says amount to blasphemy. The government puts the issue down to a clerical error.
A spokesman for the Labaik party, Ejaz Ashrafi, said the group would not comply with the deputy commissioner's ultimatum.
"We're not moving," he told Reuters by phone from the sit-in.
Pakistan's Interior Minister Ahsan Iqbal appealed to the protesters to end the sit-in before a delegation of Chinese investors arrived in Islamabad on Monday, making a last offer to negotiate on their demands.
But he added: "If some group tries to hold the state hostage, that behaviour will not be tolerated."
A government official, Khalid Abbasi, said protesters on the road were carrying rods and sticks. Since they were given the warning, he said, hundreds more party workers had joined the sit-in.
The government has blocked several roads with shipping containers in an effort to corral the protesters, causing hours-long traffic jams in and around the capital.