DES MOINES, Iowa (AP) — A group has taken out a billboard ad down the block from Republican Sen. Chuck Grassley’s Des Moines offices calling on the Senate Judiciary Committee chairman to allow an independent investigation of the Trump campaign’s possible ties to Russia.

The digital billboard around the corner from Grassley’s regional office in Des Moines began displaying the ad on Monday. Between images of President Donald Trump and Vladimir Putin, the message reads, “Sen. Grassley: America needs an independent investigation.”

The political action committee 4DPAC paid $1,100 to flash the message for a week above Court Avenue, a busy downtown street lined with bars and restaurants that is a half-block from Grassley’s office in a federal building.

“We did this because I wanted to put a very clear message next to his office to say, this is an issue his constituents really care about,” said Jim Arkedis, who heads the PAC.

Arkedis, a former Defense Department intelligence analysist, said the PAC wants to encourage Grassley to support an independent investigation of possible ties between Trump and Russia in addition to multiple inquiries underway in the House and Senate. He hopes the sign will encourage Iowa voters to call Grassley’s office and will raise the issue with the senator’s staffers.

Arkedis said 83 donors from around the country contributed a total of $1,670 after his group sought donations for the sign, which alternates with ads for the state lottery, cellphones and an upcoming Katy Perry concert.

Grassley has said that he thinks it’s too early to seek an independent investigation and expressed concern that such an inquiry could delay other investigations already started. Grassley has sent a request to Deputy Attorney General Rod Rosenstein and acting FBI Director Andrew McCabe seeking a briefing on the bureau’s Russia investigation, since the Judiciary Committee provides oversight of the FBI.

A spokeswoman for Grassley didn’t immediately respond to an email seeking comment on the billboard.