A mobile billboard has been parked at locations around Canberra for a few weeks, campaign manager Arthur Potter said, and he denied the billboard implied Labor backed a death tax policy.

Mr Potter and Liberal candidate for Bean Ed Cocks were both unaware on Tuesday that shadow treasurer Chris Bowen had ruled out introducing inheritance taxes on Monday.

Mr Potter is listed on the billboard's authorisation message.

Last week Labor asked Facebook to act on a series of posts and messages claiming a deal with the Greens and unions to introduce a 40 per cent inheritance tax had been made.

The Greens have removed inheritance taxes from their party's platform.

It was shared by an independent candidate, and Nationals MP George Christensen also shared multiple posts saying the unions demanded a death tax from Labor.

Asked if the Canberra Liberals would remove the wording from the billboard to separate his party's message from the fake news campaign, Mr Potter said "no, because I think people are a lot smarter than that".

He conceded if Labor was involved in furthering fake news about Liberal policies he'd be "going hard to get them to change it".

The Labor Party isn't "pure", Mr Potter said.

"They do this all the time, they try and link the Liberal Party to every kind of wacko extremist group they can."

Mr Cocks also defended the billboard on Tuesday, saying "it would have to be a reflection on the union's push for death taxes, and the volume of taxes that we'll be facing under the Labor agenda".

Mr Cocks rejected the idea that the billboard was misleading.

"If you look at the direction of the policy debate on that side of politics, it's certainly something that's been floated as a live option. It's certainly something that's been on the agenda and has been pushed for from that side of politics," he said.

Mr Cocks said he wasn't familiar with all of Labor's policies, and wasn't aware of the fake news articles on Facebook suggesting Labor was proposing a death tax.

He also said he would welcome Labor saying they would never introduce the policy, even though Mr Bowen had already ruled it out.

The billboard features images of both Labor leader Bill Shorten and ACT Chief Minister Andrew Barr, saying: "If you think rates are high now, just wait...".

"Labor will tax your rent, your car, your home, your retirement," it says.

"It's really highlighting the fact that living in the ACT is a very expensive proposition. It's really just highlighting the fact that we're being taxed multiple times at multiple levels," Mr Potter said.

He pointed to increases in rates, particularly commercial rates, as a reason for Mr Barr's inclusion.

Labor shadow assistant treasurer and member for Fenner Andrew Leigh said he had ruled out a death tax and accused the prime minister of lying.

"I ruled out an inheritance tax when Scott Morrison wouldn't. I've ruled it out publicly multiple times, but it appears the truth won't stop the Liberals from lying to the public," he said.