Beijing has sponsored cut-price trips to China for hundreds of Taiwanese politicians ahead of key elections on the island, according to Taiwan sources and documents, unnerving officials with a broad campaign that one called “election interference”.

President Tsai Ing-wen and other Taiwan officials have warned that China might try to sway voters toward candidates seeking closer ties with Beijing in the elections, which could define the island’s relations with China. But the scale of the Chinese activity has not previously been reported.

Beijing, which claims democratically governed Taiwan as its own and has ramped up military and political pressure to force the island to accept its sovereignty, frames the Jan. 13 presidential and legislative elections as a choice between “peace and war”, calling the ruling party dangerous separatists and urging Taiwanese to make the “right choice”.

Taiwanese law forbids election campaigns from receiving money from “external hostile forces”, including China, and prosecutors in southern Taiwan this week said they were investigating 22 people, including grassroots politicians, for potential violations of election and security laws.