Opposition leader Aung San Suu Kyi has been warned to stop calling her country "Burma".
Authorities told her she should use the constitutionally-decreed title the Republic of the Union of Myanmar.
The country's former military rulers changed the name in English from Burma to Myanmar in 1989, as they said it better reflected the country's ethnic diversity.
The term Burma connotes Burman, the dominant ethnic group in the country, to the exclusion of ethnic minorities.
But regime opponents and exiles from a range of ethnic groups - as well as foreign governments, including the UK and the United States - have persisted in using the word Burma as a sign of protest and defiance against an undemocratic regime they long saw as illegitimate.
Myanmar's election commission, which supervises laws dealing with political parties, issued the complaint in the state-run New Light of Myanmar newspaper.
The statement cited Ms Suu Kyi's repeated reference to the country as Burma during her landmark trips in recent weeks to Thailand and Europe, and said she and her National League for Democracy Party must "respect the constitution" and use the proper name.
Ms Suu Kyi was elected to the Burmese parliament when her party won dozens of seats in April's by-elections - a vote that was symbolic of the post-junta changes that have swept the country under the leadership of President Thein Sein.
Weeks later, she and her opposition colleagues took the oath of office, which includes an official vow to uphold the constitution.
Ms Suu Kyi's party spokesman Nyan Win said the election commission's complaint was a non-issue. "Referring to the country as Burma does not amount to disrespecting the constitution," he said.
In the official state language, the country and its people are both pronounced Myanmar.