Barcelona are to report Manchester United to Fifa over their signing of teenage defender Gerard Pique.
Barca are unhappy that the 17-year-old centre-back - a product of their youth academy - agreed a five-year contract at Old Trafford this week.
"United have failed to respect the effort some clubs are making in bringing on young players," Barcelona president Joan Laporta said.
"We'll see this through to the end," he told Spanish paper El Mundo Deportivo.
But Pique, a Spanish under-17 international, said he was free to join United.
"You can see that Barca don't want to negotiate," he told Radio Catalunya.
"They say I belong to them, but I'm not a slave. If they
don't want to negotiate then Fifa will have to decide what United have to pay."