"Modi ji, your government has detained me for 28 hours without any order or FIR. But those who crushed farmers have not yet been arrested. Why?" she tweeted in Hindi.
Priyanka Gandhi Vadra was taken into police custody early on Monday morning in the Hargaon area in Sitapur while she was on her way to Lakhimpur Kheri to meet families of the deceased farmers.
After a brief spat with the policemen, Priyanka was taken to the PAC guest house and remains there till now.
Hundreds of Congress workers have been sitting outside the guest house, waiting for their leader's release.
Priyanka has said that as soon as she is released, she will proceed to Lakhimpur Kheri to meet the bereaved families.
In a related development, a senior official said that the government has taken note of the fact that Priyanka spoke to some news channels on phone while she was in custody.
"We are investigating the matter and will soon take action against the channels and those responsible for arranging the interactions," the official said.