The unnamed Cathay Pacific flight attendant said on her Facebook page that she almost flew into a rage when her supervisor told her not to pour coffee on Paetongtarn Shinawatra, the youngest daughter of Thaksin Shinawatra.
A report by the South China Morning Post newspaper said the flight attendant caused a stir in Thai online communities last week when she posted hostile comments about Paetongtarn Shinawatra.
The flight attendant, whose Facebook handle is Honey Lochanachai, said she resigned to take responsibility.
Her Facebook post reportedly showed a photo of the passenger list for a Hong Kong-bound Cathay flight from Bangkok on Nov. 25, on which the attendant came across Paetongtarn's name.
"I never expected that (Paetongtarn) was on board today," the post read. "I immediately told my flight manager I couldn't work knowing the daughter of my enemy was on the plane. I called my personal adviser asking if it would be all right to throw coffee at Paetongtarn but was told that this could breach Hong Kong's laws.
"I was so angry and could not come to terms with the failure of (last month's) anti-government rally in Bangkok."
The Hong Kong airline posted on its Thailand Facebook page that the flight attendant is "no longer an employee," the Morning Post said.
Thaksin, 62, was ousted in a military coup in 2006 and soon after was sentenced to two years in prison for tax fraud. He fled in 2008 rather than serve his sentence, leaving an estimated $2 billion in frozen assets, and lives in Dubai.
Thaksin's sister, U.S.-educated Yingluck, 45, was elected as Thailand's first female prime minister in July 2011. However, Yingluck's's political experience is limited, leading critics to claim that Thaksin holds the actual reins of power from Dubai.
At the end of November, leaders of an anti-government protest by thousands of demonstrators called off their march in the Thai capital Bangkok amid fears of further clashes with police.
Police defended the firings of tear gas at protesters at two roadblocks, saying a large number tried to break into Government House, a report by Thailand's The Nation newspaper said.
Police said the protesters failed to follow police's warnings and some of them began to cut away police barbed wire barricades.
"We had no choice but to fire tear gas at the protesters," police said.
The protesters believe the government is corrupt and they want new elections.