Will.i.am says a trademark that Pharrell's company tried to register is too similar to his "I AM" trademark.
Will.i.am has owned the "I AM" trademark since 2001. He filed objections in March and May against Pharrell Williams' company, i am OTHER, that launched in 2010.
In a statement Thursday, will.i.am's attorney Ken Hertz said trademark lawyers for the singer-songwriters have discussed the disagreement for several months. They first spoke in December, he said.
Hertz said that because of the U.S. Patent and Trademark Office's deadlines, will.i.am "had no choice but to lodge his objection at the time he did."
Pharrell said in a statement that he was disappointed and surprised by will.i.am's objection.
"The plain truth is that Will has obstructed every overture made by Pharrell to amicably resolve this matter and has steadfastly refused to engage in a dialogue," said Pharrell attorney Brad Rose in a separate statement.
Will.i.am uses "I AM" for his businesses, including his charity foundation I AM ANGEL.
Pharrell's i am OTHER produces the hit web series "Awkward Black Girl" and other web series.