The parents and sister of Shahawar Matin Siraj, who was sentenced Monday for plotting to blow up the subway station at Herald Square, have been detained on immigration violations, a lawyer for the family said yesterday.

They were arrested yesterday, as headlines announced Siraj’s 30-year sentence appeared in city newspapers.

Siraj’s mother, Shahina Parveen, and his father, Siraj Rehman, frequently attended their son’s legal proceedings and were present at Monday’s sentencing.

A spokesman for Immigration and Customs Enforcement could not be reached to confirm the arrests late last night.

Immigration authorities have long been aware that members of Siraj’s family, who live in Queens, had overstayed their visas. It was not immediately clear why immigration authorities chose the day after the conclusion of Siraj’s closely watched criminal case to arrest his mother, father, and sister.

“The government wanted to show an iron fist,” the attorney for the family, Mona Shah, said of the three arrests. “This is just so wrong.”