Republicans: Change consumer bureau ... or else

NEW YORK (CNNMoney) -- Republican senators have fired another broadside at the Consumer Financial Protection Bureau, vowing to block the nomination of any candidate to lead the watchdog agency without major structural reforms.

For the Obama administration, it's the latest roadblock in what has become a marathon search for a director to head the agency that was a key component of last year's Wall Street reform law.

Born out of the financial crisis, the consumer bureau has its own funding and will regulate financial products such as mortgages and credit cards starting July 21.

On Thursday, 44 of the 47 Republicans in the Senate sent a letter to President Obama, arguing that the new agency is far too powerful, and lacks structural checks and balances that would make it more accountable.

For the White House, the math is daunting. With nearly every Republican a signatory to the letter, there won't be enough votes to end a filibuster and bring a nominee up for a vote.

Republicans want changes at the very top of the agency. The director -- a position that sits vacant -- would be replaced with a board.

Big business: Go slow on consumer bureau

Also at issue: exactly who that single person is.

Without mentioning her by name, the letter is a thinly veiled reminder to the White House that an attempt to nominate Democrats' favorite candidate, Elizabeth Warren, would lead to a contentious fight on the Hill.

Officially a White House adviser who also works with the Treasury Department, Warren is a lightening rod figure in the fight over the future of the agency.

It's no secret that the White House would love to nominate her to lead the agency. Republicans are less thrilled with the idea.

Just last week, the outspoken Warren lambasted Republican tactics during an appearance on "The Daily Show with Jon Stewart."

"Now the game is, let's just see if we can stick a knife in the ribs of this consumer agency," she said.

On another front, the House Financial Services Committee is considering bills to prevent the bureau from flexing new powers.

In defending the agency on the show, Warren harkened back to the plain-spoken, heartfelt attacks that won her such broad public support as a consumer advocate.

"Right now there are bills pending in Congress to delay the agency, to defund the agency, to defang the agency, make it toothless, so it won't get anything done," she told Stewart. "And bills to kill the agency outright before it is ever able to take one step on behalf of middle class families."

Amy Brundage, a spokeswoman for the White House, defended the agency's mission.

"The consumer agency's sole mission is to protect American families and provide the tools they need to make smart financial decisions," Brundage said. "American families who were the hardest hit by this financial crisis deserve an independent watchdog to protect consumers and prevent predatory lending and other abuses in the future."

-- CNNMoney senior writer Jennifer Liberto contributed to this story