Ecuador has lodged a complaint with World Cup organizers about noisy local fans outside their team hotel before their round of 16 match against Mexico.
Local media reported that about 1,000 Mexican supporters staged a raucous “serenade,” a musical performance dedicated to honor or an expression of love, in Mexico City on Monday.
The match will take place on Wednesday (02:00 BST) at Mexico City Stadium.
Noise makers, pots and buckets were used to sing the Mexican folk song “Cielito Lindo” before police took them back.
“This behavior is far from the principles of fair play, equality and unity that the World Cup should represent,” the Ecuadorian Football Federation said in a statement.
The statement added that Ecuador “will always respond on the pitch.”
Mexico won all three World Cup games at Mexico City Stadium, and Ecuador’s shock victory over Germany secured their place in the knockout stages.
“We believe that these unsportsmanlike actions will not tarnish the football festival that unites two fraternal countries,” the statement said.
England, who play DR Congo on Wednesday (17:00 BST), will play Mexico in Mexico City if both teams win their last 32 games.
FIFA has been contacted for comment.