Vice President Joe Biden will attack Mitt Romney on taxes in Exeter, N.H. today, using his fourth in a series of campaign issue speeches to frame the Republican candidate as a protector of the rich.

Biden will coin a new phrase - "the Romney Rule" - to illustrate his case, according to excerpts of his remarks released by the Obama campaign.

"The Buffett Rule says that multi-millionaires should pay at least the same percentage of their income in taxes as middle-class families do," Biden will say.

"The Romney Rule says the very wealthy should keep the tax cuts and loopholes they have, and get an additional, new tax cut every year that is worth more than what the average middle class family makes in an entire year."

Biden refers to the so-called Bush tax cuts on individuals earning more than $200,000 and families making more than $250,000. Romney wants to extend and expand the cuts, which are set to expire at the end of the year; Obama wants to let them lapse.

"Look, these are tax cuts to people who didn't ask for them, who don't need them, and who know the nation can't afford them," Biden will say. "And it matters. There's a stark choice we have to make."

By raising the Bush-era cuts, Biden adds a new dimension to the ongoing tax debate in Washington and on the campaign trail that has recently been focused solely on the Buffett Rule. It also expands the scope of impact of Democrats' calls for higher taxes, from a small fraction of the top 1 percent of taxpayers to roughly 3 percent of all taxpayers.

President Obama has been making the case that higher taxes on wealthier Americans is a matter of fairness and one that will help trim the deficit and underwrite "investments" in services to benefit the middle class. Biden will underscore those themes.

The Romney campaign plans to bracket Biden's speech, dispatching spokesman Ryan Williams and former New Hampshire Gov. John Sununu to Exeter Town Hall, while the Republican National Committee has begun preemptively slamming the message.

"Instead of the 'Buffett Rule,' the real issue is the 'Obama Rule,'which is President Obama's plan to raise taxes on American families and small businesses to grow government and stifle free enterprise," said Romney spokeswoman Andrea Saul.

RNC chairman Reince Priebus accused the Obama-Biden campaign of engaging in class warfare. "That's the only card left in Obama's hand," Priebus told reporters Wednesday. "We think that this plan is going to backfire however and especially when you look at new polling showing that independents actually favor economic opportunity."

The New Hampshire address caps Biden's debut tour on the 2012 campaign trail. He used previous appearances to defend the administration's record on the auto bailout in Toledo, O.H.; tout a resurgence in manufacturing jobs in Davenport, Iowa; and tweak Republicans' plans to overhaul Medicaid in Coconut Creek, Fla.

This post has been updated.  ABC News' Emily Friedman contributed to this report.