MANILA -- A week after Philippine President Rodrigo Duterte savaged two listed companies with the words "I can ruin your face, son of a bitch," close to $1 billion has been wiped from their market value.

Alarmed investors have steadily dumped shares in Manila Water Company and Metro Pacific Investments, the parent of Maynilad Water Services, since Duterte's angry response on Dec. 3 to a court ruling ordering his government to pay 7.4 billion pesos ($145m) in arrears.

The sell-off intensified on Wednesday after the state water regulator said contracts with Manila Water Company and Maynilad Water Services would end in 2022, instead of 2037. Shares of Manila Water continued to sink on Thursday morning while those of Metro Pacific steadied.

Duterte's strong-arm gambit will likely spook markets at a time when foreign investors appear to be losing confidence in the Philippines amid the prolonged US-China trade war. Foreign direct investment plunged to $5.1 billion from January to September 2019, a 37% drop compared to the same period the year before, the Philippine central bank said on Tuesday.

"This is not good in the eyes of foreign and even local investors, that the government is reneging on its contractual obligations," said Astro Del Castillo, managing director at investment company First Grade Finance in Manila. "The damage has been done, investors might now see having contracts with the government as a risk factor."

Known for his quick temper, Duterte is prone to lashing out against people who cross him. Shares of the Philippines' largest broadcaster ABS-CBN have also yet to recover after Duterte, angered by the media company's coverage, said last week that the company's legislative franchise would not be renewed when it expired next year.

The water dispute however also involves powerful foreign groups. Controlled by powerful Ayala conglomerate, Manila Water has Japan's Mitsubishi as a strategic investor. Meanwhile Metro Pacific is a Philippine unit of Hong Kong-listed First Pacific, which is controlled by Indonesia's Salim Group.

The argument was sparked last month when a Singapore arbitration court ordered Duterte's government to compensate Manila Water for being unable to implement rate increases, as stipulated in their concession agreement.

Both companies subsequently agreed to waive the back payments, following Duterte's outburst. Nevertheless, the state water regulator cancelled previously agreed extensions to the concession periods' for both companies.

That means the lucrative rights to provide water serices to metropolitan Manila will be up for grabs in 2022 and could be awarded to new companies.

This is not the first time that Duterte has taunted tycoons. Upon assuming the presidency in 2016, Duterte named tycoon Roberto Ongpin as an "oligarch," who he wanted "to destroy." Shares in Ongpin's online gaming company, PhilWeb, subsequently collapsed.

In 2017, Duterte also threatened to shut down Philippine Airlines' terminal at Manila airport terminal if the carrier did not settle an unpaid tax bill.

After the company agreed to pay 6 billion pesos to the government, Duterte and Philippine Airlines owner Lucio Tan became friends, with the president attending the tycoon's 85th birthday bash last year.

"That's just the style of the president: strong rhetoric, then he tones down, then he finds a middle ground," said First Grade Finance's Del Castillo.