TAIPEI (REUTERS) - Thousands of people thronged Taipei's streets on Sunday (Nov 22) for the annual "Autumn Struggle" protest march organised by labour groups, with much of the anger focused on the government's decision to ease restrictions on imports of United States pork.

Taiwan's main opposition party, the Kuomintang (KMT), rallied its supporters to join in the march for the first time, having mounted an increasingly strident campaign against the pork move, which it says threatens food safety.

President Tsai Ing-wen announced in August that the government would from Jan 1 allow in US pork containing ractopamine, an additive that enhances leanness but which is banned in the European Union and China, as well as US beef more than 30 months old.

While welcomed in Washington, and removing a roadblock to a long sought after US free trade deal for Taiwan, the KMT has strongly opposed the decision, tapping into public concern about food safety after several high-profile scandals in recent years.

KMT chairman Johnny Chiang, elected in March to help turn around party fortunes following a trouncing in January's presidential and Parliament elections, called on Ms Tsai to have a televised debate with him about the issue.

"Taiwanese pigs don't eat ractopamine, and yet you are asking Taiwanese people to? Does this make sense?" he told supporters.

There was no immediate reaction from the presidential office.

Ms Tsai's government and her ruling Democratic Progressive Party (DPP), which has a large majority in Parliament, say the decision brings the island into line with international norms, is not a safety threat and will boost Taiwan-US ties.

The DPP, which had previously strongly objected to ractopamine, has accused the KMT of spreading fake news about the subject trying to sow public fear.

The KMT is also trying to organise a referendum on the US pork imports for next year.

The pork is due to start arriving from Jan 1.