The new book by ex-Treasury Secretary Timothy Geithner is out, and is already getting push-back from a prominent Republican economist.

Glenn Hubbard, an aide to President George W. Bush and 2012 Republican candidate Mitt Romney, said Geithner is making up a story claiming that Hubbard said Republicans would eventually have to raise taxes.

Geithner is "going to go out and say what he wants," Hubbard told Politico. "It just happens to be a lie."

In his book "Stress Test", which details the Obama administration's response to the financial crisis, Geithner writes that Hubbard complained about the White House refusal to endorse the Simpson-Bowles deficit reduction plan.

Noting that Simpson-Bowles includes proposed tax hikes, opposed by Republicans, Geithner writes that he told Hubbard: "When you guys are willing to raise taxes, we can talk about Simpson-Bowles."

According to Geithner, Hubbard responded: "Well, of course we have to raise taxes -- we just can't say that now."

Geithner's book was published today (May 12, 2014)

Hubbard, now the dean of Columbia Business School, told Politico that Geithner made up the story:

"'It's pretty simple. It's not true,' Hubbard said when reached by phone.

"Hubbard, who said Geithner did not reach out to him before the publication of the book, said he remembers having a conversation about the Simpson-Bowles plan.

"'I was asking him something like, how can Romney's plan be off base because it's essentially the Bowles-Simpson structure and Bowles-Simpson actually raises revenue,' Hubbard said. 'But I wasn't suggesting that we're trying to raise taxes.'"