The US Senate has voted in favour of making English the national language.
The language issue is part of an immigration debate dividing the US
The measure, backed by Republicans, came as an amendment to a controversial immigration bill currently going through the Senate.
Lawmakers voted by 63-34 in favour of the move, which calls on the government to "preserve and enhance the role of English as the national language".
But the Senate also approved a milder Democrat amendment describing English as the "common and unifying language".
Neither of the bills would bar the use of Spanish or other languages in government services.
'Preserving our culture'
The BBC's Emilio San Pedro, in Miami, says the issue of the preservation of the English language and American culture is for many at the heart of the immigration debate in the US.
Many Americans are concerned that the influx of immigrants from the Mexican border are altering the very fabric of American life, our correspondent says.
US ILLEGAL IMMIGRANTS
About 11.5m illegal immigrants in the US
Four out of 10 have been in US five years or less
75% were born in Latin America
Most enter via southern US border
California, Texas and Florida host most illegal immigrants
Many work in agriculture, transport and construction
"This is not just about preserving our culture and heritage, but also about bettering the odds for our nation's newest potential citizens," said Oklahoma Republican James Inhofe, who sponsored the national language amendment.
Sen Inhofe said polls show around 80% of Americans would support a move to formalise English as the national language.
But critics fear the move could lead to discrimination against people who are not proficient in English.
"Although the intent may not be there, I really believe this amendment is racist," said Senate Democratic leader Harry Reid. "I believe it is directed at people who speak Spanish."
Both amendments will be included in the bill that the Senate sends to the House of Representatives, where the differences will need to be reconciled.
President Bush, during a visit to Arizona to promote his immigration reform package, did not specifically endorse the move but stressed the need for unity.
"Americans are bound together by shared ideals and appreciation of our history, of respect for our flag and ability to speak the English language," he said.
Mr Bush has proposed tightening border security while giving many existing illegal immigrants the right to stay. Many Republicans say the plan is too soft, arguing that illegal immigration should be criminalised, while Central American states have attacked the US proposal to build hundreds of kilometres of fencing along its border.