Billboards calling on Republican Gov. Chris Christie to denounce Donald Trump are popping up across New Jersey.

Bridges Over Politics for New Jersey, a new nonprofit advocacy group, said Friday it has spent six figures for about a dozen billboards and digital ads across the state.

One of the ads shows the Republican presidential candidate with Christie behind him. The text asks Christie to "stand up to racism and bigotry."

Trump has drawn criticism from rivals for pledging to build a wall to keep Mexican immigrants from entering the country illegally and for failing to immediately denounce Ku Klux Klan leader David Duke, who said not voting for Trump was "treason to your heritage."

Christie endorsed Trump after his own presidential campaign ended in failure. He has said he doesn't agree with Trump on everything, but that Trump gives the party the best chance to defeat Democratic front-runner Hillary Clinton in the fall.

The billboards are in Bergen, Hudson and Mercer counties. The group is headed by Aaron Keyak, a one-time aide to former Democratic U.S. Rep. Steve Rothman. The group's donors are not public.

"It's a very serious issue," Keyak said "This isn't a regular political disagreement like how high or low tax rates should be."

Christie's office responded to the ads arguing that there's nothing to see there.

"What's sad is that anyone would give this a second look," spokesman Brian Murray said.