The UNP's Vijayakala Maheswaran, the state minister for child affairs has refused to hoist the Sri Lankan flag at a function in Jaffna on Monday night.
Ms Maheswaran, who is Tamil, was the chief guest at the opening of a science lab in the Meesalai Veerasingam College in Thenmaratchi, in the Jaffna district.
"I have been a member of parliament for six years. However not one day have I hoisted the lion flag out of principle and I will not give up on this principle," she said.
Ms Maheswaran's husband, also a UNP MP, was killed by government-aligned paramilitaries in 2008.
Sri Lanka's flag is seen as controversial by many Tamils in the North-East of the island, due to its Sinhala Buddhist symbolism and its use throughout the armed conflict for state triumphalism and oppression.