It vowed "punishment" and announced military drills, including live-fire exercises, expected to begin at 0400 GMT in several areas encircling Taiwan.
EU foreign policy chief Josep Borrell, in Phnom Penh for talks with ASEAN, condemned the Chinese response.
"There is no justification to use a visit as pretext for aggressive military activity in the Taiwan Strait. It is normal and routine for legislators from our countries to travel internationally," he tweeted.
Kung Phoak, Cambodia's deputy foreign minister and ASEAN spokesman, urged both sides to stabilise the situation.
"We hope de-escalation happens... and normalcy returns to the Taiwan Strait," he told reporters.
ASEAN is split between countries with close ties to China, such as Myanmar, Cambodia and Laos, and others that are warier of Beijing and its growing international assertiveness.
But no ASEAN country formally recognises Taiwan and none have shown an appetite for backing Taipeiagainst the communist giant.