Lawyer Matthias Chang will challenge his detention under the Security Offences (Special Measures) Act (Sosma).

His lawyer, Hanif Khatri Abdullah, said they plan to file the application in court on Monday.

"We are already preparing the documentation and we shall get the affidavit ready tomorrow.

"We will file it in court as early as Monday morning when court opens and see if we can get it fixed on the same day as Khairuddin Abu Hassan's application," Hanif ( photo ) told reporters outside the Dang Wangi district police headquarters today.

Chang was arrested under Sosma yesterday for offences under Sections 124K and 124L of the Penal Code.

Section 124K and 124L deal with sabotage and attempting to sabotage the state, respectively.

Chang's remand under the anti-terrorism law has been extended to 28 days starting today.

Hanif said Chang was still on hunger strike, but is in high spirits.

The lawyer was arrested yesterday, for acting as Khairuddin's counsel when the former Batu Kawan Umno deputy chief lodged reports against 1MDB with several security agencies overseas.

The duo had first been barred from leaving the country on Sept 18, and Khairuddin was arrested under Sosma later that night.