Maryam Nawaz Sharif, a leading figure in Pakistan's political opposition, has been arrested by anti-graft authorities.
She was visiting her father, the jailed former Prime Minister Nawaz Sharif, when she was taken into custody.
The country's National Accountability Bureau (NAB) said she was being held in connection with a money laundering investigation.
Her PML-N party said the arrest was politically motivated.
Ms Sharif's cousin, Yousaf Abbas Sharif, was also arrested. The pair will appear before a Lahore court on Friday.
In a brief statement the NAB, an anti-corruption watchdog, said that Ms Sharif was detained in connection with a corruption investigation involving a sugar mill owned by the Sharif family.
Ms Sharif has led several large political rallies in recent weeks and is a vocal critic of Prime Minster Imran Khan and Pakistan's powerful military.
Parts of her speeches at these rallies have been muted during television broadcasts within Pakistan, but Mr Khan and the military have denied accusations of censorship.
Nawaz Sharif, a three-time prime minister, is serving a seven-year sentence for corruption. He was disqualified from office in July 2017 and his brother, Shahbaz Sharif, is now the PML-N leader.
Ms Sharif was released on bail last year after her own corruption sentence was suspended.
Earlier this year, she released a secretly recorded video of one of the judges who had convicted her father, apparently admitting he had been blackmailed into finding him guilty.
The judge subsequently denied the claims, saying the video had been "edited" but a number of channels which broadcast Ms Sharif's news conference were later taken off air for several days.
The Sharif family has dominated Pakistani politics for decades and has been embroiled in several high-profile corruption cases.
The family says the cases are motivated by politics. Pakistan's government and military deny this.
Ms Sharif's latest detention comes just a day after the arrest of former finance minister and Sharif family loyalist Miftah Ismail, who was also accused of graft.
In recent months, former prime minister Shahid Khaqan Abbasi and former president Asif Ali Zardari have also been arrested by Pakistani authorities.