Taipei, Feb. 25 (CNA) The ruling Democratic Progressive Party (DPP) voted on Thursday to suspend three of its lawmakers who defied the party last December by abstaining from a series of votes regarding the lifting of restrictions on imports of pork containing the controversial feed additive ractopamine.

DPP legislators Lin Shu-fen, Chiang Yung-chang and Liu Chien-kuo were each suspended from running for party leadership positions for a period of one year as a result of their breach of party discipline during the Dec. 24 voting.

They could face much heavier punishment -- a three-year suspension -- if they breach party discipline in a similar fashion again, according to the party's decision released following a DPP Standing Evaluation Committee meeting that day.

The three had already been given fines of NT$30,000 (US$1,069) each and had been banned from serving in leadership posts in the DPP's legislative caucus for three years in December by the party's legislative caucus.

The issue stems from a series of votes the Legislature held on Dec. 24, in which it approved nine directives related to President Tsai Ing-wen's Aug. 28 announcement that Taiwan would soon allow imports of pork containing "acceptable levels" of ractopamine, a leanness-enhancing feed additive, as well as U.S. beef from cattle aged over 30 months.

The policy, which took effect on Jan. 1, is widely viewed as an effort by the government to satisfy U.S. prerequisites for any negotiations on a bilateral trade deal.

However, it has caused dissent among some in the DPP who strongly opposed even traces of ractopamine residue in pork during the previous administration of President Ma Ying-jeou from 2008-2016.

The three lawmakers reportedly decided to abstain, as most of the people in their constituencies are opposed to the new policy.

Critics of the decision to allow pork containing ractopamine into Taiwan argue that it fails to prioritize the health of Taiwanese or the interests of local pig farmers, despite reassurances from the government.