[Taipei] Taiwan has threatened to revoke passports that have been altered after pro-independence activists used stickers to change them and successfully travelled abroad.
The sticker campaign has seen activists cover the "Republic of China" logo on their passports with stickers saying: "Republic of Taiwan".
Taiwan is self-ruling after splitting with China in 1949 following a civil war, but has never formally declared independence. Beijing sees it is a renegade province awaiting unification, by force if necessary.
The island calls itself the Republic of China, but independence campaigners say they want a clearer distinction between Taiwan and the mainland.
The sticker campaign comes as fears are growing over the increasing influence of Beijing, following a rapprochement under Taiwan's current president Ma Ying-jeou.
Taiwan announced on Tuesday that it had amended regulations and could revoke the passports of those who repeatedly alter them.
It also threatened a delay in renewing expired passports if they have been altered.
The foreign ministry denied the new measures were politically motivated.
"The idea of amending the regulations sprung up several years ago, before the use of pro-independence stickers. It has nothing to do with politics," said foreign ministry spokeswoman Eleanor Wang.
"Any tampering of passports could increase the difficulty of border controls and undermine the credibility of our passports," she added.
Around 250,000 "Republic of Taiwan" stickers have been sent out since the start of the campaign in July, according to the Taipei Times.
The sticker's designer, who the newspaper said named himself as Lao Tan, described it as a national identity movement.
Pro-independence groups reacted angrily to Tuesday's announcement.
"The government is trying to use punitive measures to threaten Taiwanese people, but for me, they don't work, I'll keep doing this," Tsay Ting-kuei, chairman of the pro-independence Free Taiwan Party, told AFP.
Mr Tsay says he has travelled to a number of countries using the altered passport.
"Customs officials of other countries are easily confused between the 'Republic of China' and 'People's Republic of China' in Beijing," Tsay added.
There is no official count of how many times the doctored passports have been used.