Uruguay's government asked Congress on Friday to allow US troops to stay in country during the upcoming G20 meeting in neighbouring Argentina, due to be attended by the US and Russian leaders.
Washington wants to send 400 civilian and military personnel as well as eight aircraft for a week, from November 26 to December 3.
US President Donald Trump and Russia's Vladimir Putin are scheduled to attend the event.
Uruguay's Defense Ministry submitted a two-part bill to Congress, the first of which sought permission for the US troops, official sources said.
The bill's second article asks for authorization to allow troops from other countries whose leaders are attending the summit to be stationed in Uruguay, according to a document seen by AFP.
Opposition senator Javier Garcia told AFP that such authorization can only be issued by the General Assembly through a constitutional mandate.
But he stressed that any such authorization would be for a specific request rather than a "carte blanche" opening of doors to unspecified foreign troops.
Garcia said the Defense Ministry would have to ask each other country wishing to use Uruguayan soil to provide a detailed request similar to the one US officials presented.
The G20 summit takes place in the Argentine capital Buenos Aires, which is just 200 kilometers (125 miles) away from Uruguay's capital Montevideo.