Thailand gets more than half of its foreign direct investment from Japan. That foreign capital brings much-needed money into a country that recorded a current account deficit in 2013 and may again this year.
It is the biggest car market in Southeast Asia and a regional production and export base for top manufacturers such as Toyota, Nissan Motor and Ford Motor.
It is also a major global production center for hard disk drives with big players such as Seagate Technologyand Western Digital having operations in the country.
Thai partners are putting a brave face on things.
Hemaraj Land and Development runs seven big industrial estates, home to factories for the likes of Ford Motor, General Motors and Caterpillar.
David Nardone, its chief executive, said 10-20 percent of new customers had postponed signing contracts to take up facilities since December.
"It's short-term disruption," Nardone said, hopeful there would be a recovery in the next few months. "There may be some people who don't know Thailand so well and they may take longer, have more questions and wait for clarity."
The optimists point to 2010, when more than 90 people died in another protracted bout of political unrest. Foreign direct investment jumped 88 percent that year, the stock market surged 41 percent and the economy bounded ahead by 7.8 percent.
This time, however, the protests have gone on for three months and government work is being disrupted.
Some $60 billion of infrastructure spending may not get started this year, for example. Consumer confidence fell for the ninth month in December to a two-year low and investors worry about a possible escalation of violence, which will hold back Southeast Asia's second-largest economy after Indonesia.
Politics and Floods
"Political instability is always preventing investment flows. Long term investments projects may be reconsidered and other locations may be reassessed," said Rolf-Dieter Daniel, President of the European ASEAN Business Centre, which groups 14 European chambers of commerce in Thailand.
Foreign direct investment probably totaled almost $13 billion in 2013 but could drop to less than $8 billion in 2014 even if tension eased and investors returned in the second half, said Pimonwan Mahujchariyawong, an economist at Kasikorn Research Center in Bangkok.
Investment also dropped in 2011 when widespread flooding disrupted the activities of global electronics and car firms.