Donald Trump urged supporters during a conference call Monday to intensify attacks on the federal judge presiding over the Trump University case after learning a memo was sent from his own campaign to not discuss the lawsuit.

Trump stood by his attacks on U.S. District Judge Gonzalo Curiel’s Mexican ancestry and ordered supporters to question the judge’s credibility as well as intensify attacks on reporters, Fox News confirmed.

Bloomberg first reported that Trump learned about the memo during the conference call and questioned how his supporters are supposed to defend themselves when they aren’t allowed to talk.

"That's one of the reasons I want to have this call, because you guys are getting sometimes stupid information from people that aren't so smart," Trump said.

The memo, which was obtained by Bloomberg, told surrogates that “they’re not authorized to discuss matters concerning the Trump Organization including corporate news such as the Trump University case.”

Republican lawmakers are urging the presidential candidate to apologize for talking about the ethnic background and impartiality of Curiel.

Curiel is a former federal prosecutor who was born in Indiana to parents who came from Mexico in the 1940s. He has not responded to Trump's attack, and Trump's legal team has not sought his removal from the case. Judges generally are thought to have conflicts of interest only in more specific situations, such as a financial interest in the outcome of the case.

Trump University is the target of two lawsuits — in San Diego and New York — which accuse the business of fleecing students with unfulfilled promises to teach them secrets of success in real estate. Trump has maintained that customers were overwhelmingly satisfied. Curiel is presiding over the suits in California.

Fox News' Carl Cameron and the Associated Press contributed to this report.