A DA Limpopo provincial legislature member was detained on Friday for allegedly trespassing at a textbook warehouse, the party said.
Police refused to release Democratic Alliance MPL Meisie Kennedy until she had deleted photos from her phone, party leader in the province Jacques Smalle said in a statement.
"Ms Kennedy is a member of the legislature and entitled to inspect these public resources that should be in schools.
"The DA made a surprise visit to the warehouse this morning after pursuing the reasons for book shortages in schools this week," Smalle said.
Limpopo police could not immediately comment.
Kennedy said the books stacked from the ground to the ceiling in the warehouse.
"I introduced myself [and said] I wanted to conduct an oversight at the warehouse," she said.
"I was allowed in, but while taking pictures I was manhandled. I screamed, I wanted to get help. They grabbed me. I'm still in shock."
Kennedy said she would not lay a charge with police because she was not injured. Her driver's licence, ID, and camera were confiscated, but returned after the photos were deleted.
The DA said they had heard from schools with textbook shortages that the education department had failed to deliver because of problems with a tender.
Smalle said the department attempted to move the textbooks to another location on Friday morning when it heard of the DA's visit.
"A delegation including Mmusi Maimane, Desiree van der Walt, and myself arrived in time to witness this," said Smalle.
"The warehouse was immediately put into lockdown and thousands of books are still inside."
The DA wanted answers from Basic Education Minister Angie Motshekga on why thousands of books had not been delivered.