Burmese officials have told opposition leader Aung San Suu Kyi to call the country by its official name, Myanmar.
The country was renamed Myanmar in 1989 by its then military rulers and the change has been widely adopted since.
But opposition groups have continued to use the old name as a sign of defiance, along with some Western governments and media organisations.
Ms Suu Kyi was freed from arrest in 2010 and elected to parliament this year amid continuing political reforms.
She is set to return from a high-profile trip to Europe, during which she referred to her country as Burma.
She also used the term Burma during a speech to the World Economic Forum in Thailand on 1 June, apparently annoying her country's military-backed civilian government.
Correspondents say the authorities may be trying assert themselves after Ms Suu Kyi, who leads the National League for Democracy (NLD), was feted throughout her European tour.
In a statement published in The New Light of Myanmar newspaper, the electoral commission said: "As it is prescribed in the constitution that 'the state shall be known as The Republic of the Union of Myanmar', no one has the right to call [the country] Burma.
"It is announced that the commission... has again informed the NLD to write/address the name of the state as prescribed in the constitution... and respect the constitution."
NLD party spokesman Nyan Win responded by saying that referring to the country as Burma "does not amount to disrespecting the constitution".
The then ruling military chose to rename Burma two decades ago, arguing that the old name was a hangover from colonialism and only represented the dominant Burman ethnic group.
Etymologists and others suggest that this argument is false, as both Myanmar and Burma come from the same root - referring to the Burman ethnic group - and have been used interchangeably for centuries.
The US and UK governments still use Burma to refer to the country, as do some media organisations, including the BBC.