It comes after Taipei accused Beijing of "abducting" its citizens from Kenya earlier this month.
The deportations are seen by observers as a shot across the bows of Beijing-sceptic Tsai Ing-wen, who will be inaugurated as Taiwan's president on May 20.
"The government has filed solemn protests and regrets the development," presidential office spokesman Charles Chen said of the deportations today.
Taiwan would send a delegation to the mainland "as soon as possible" Chen said.
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They were part of a group of 52 Taiwanese detained by Malaysian police last month during five raids linked to telecom fraud, which also led to the arrests of 65 mainland Chinese and two Malaysians.
Twenty of the Taiwanese were deported back to Taiwan two weeks ago, where they were initially allowed to go free.
After complaints in Chinese state media, which labelled Taiwan a "haven of frauds", 18 of them were later arrested. They are currently in custody in Taiwan.
Questions had swirled over the fate of the other 32 suspects, with Taiwan saying it was negotiating with Malaysia for their return.
But the Chinese side informed Taiwan Saturday that the suspects were being deported to the mainland, the justice ministry said.
CNA reported China had invited Taiwanese officials to go to the mainland to jointly investigate the case.
Taipei blasted Beijing earlier in April for being "rude and violent" over the deportation of 45 of its citizens from Kenya to China where they face investigation for fraud.
It has also filed a suit against several top officials in Kenya for ignoring a court decision which cleared some of the suspects and "illegally cooperating" with China to deport the Taiwanese.
China considers Taiwan to be one of its provinces awaiting reunification, by force if necessary, even though the island has ruled itself since 1949 following a civil war split.