The Czech foreign ministry said Monday it had summoned the Chinese envoy to Prague after Beijing threatened an opposition politician currently on a visit to Taiwan.
A delegation led by Czech Senate speaker Milos Vystrcil arrived in Taipei on Sunday, angering China which is trying to keep the island isolated from the rest of the world.
Chinese Foreign Minister Wang Yi said on Monday that China would make Vystrcil "pay a high price for his short-sighted behaviour and political speculation", calling the journey a "provocation".
The Czech foreign ministry then said on its website that deputy minister Martin Tlapa had summoned the ambassador, expressing "fundamental disapproval" of the statement.
Czech Foreign Minister Tomas Petricek said earlier on Monday he expected China to explain Yi's words.
"Of course the journey has an impact on our relationships with China, but I think this has gone too far," he told journalists.
Czech Prime Minister Andrej Babis has labelled the statement "impertinent and inappropriate".
Beijing said later on Monday that Vice Foreign Minister Qin Gang had recently summoned Czech ambassador to China, Vladimir Tomsik, and "lodged solemn representations".
Qin said Vystrcil's visit was a "serious violation of China's sovereignty" and vowed Beijing would "make the necessary response to protect its own legitimate interests," according to a statement from the foreign ministry.
- One China policy -
The Czech government accepts the One China policy under which Beijing considers Taiwan a part of its territory, with reunification by force an option, and does not send official delegations to the island.
But Vystrcil is a member of the right-wing opposition Civic Democrats and is not bound by the protocol.
His 90-member group, including politicians, entrepreneurs, scientists and journalists, will stay in Taiwan until Friday.
He will give a speech in Taiwan's parliament on Tuesday and will meet President Tsai Ing-wen, whose re-election earlier this year upset China as she views the island as a sovereign nation.
Vystrcil said his trip would fulfil the legacy of the late Czech president Vaclav Havel, a human rights fighter and dissident leader of the 1989 Velvet Revolution which toppled communism in the former Czechoslovakia.
Vystrcil is following in the footsteps of his predecessor Jaroslav Kubera, who died of a heart attack in January while planning the Taiwan visit.
After Kubera's death, Czech media published a letter stamped by the Chinese embassy in Prague and which threatened both Kubera and Czech companies intending to accompany him on the trip.
Ties between Prague and China suffered a blow last October when Prague city hall, run by a mayor from the anti-establishment Pirate Party, pulled out of a twinning deal with Beijing over its insistence on the One-China policy.
Prague mayor Zdenek Hrib, who is on Vystrcil's delegation, then signed a partnership agreement with Taipei in January, triggering outrage in Beijing.