Jim Wilson/The New York Times

SALEM, N.H. — Mitt Romney on Thursday branded President Obama a “crony capitalist” for making three appointments to the National Labor Relations Board without Congressional approval, suggesting the move was a reward to organized labor for its political support.

“This president has engaged and is engaging in crony capitalism,” Mr. Romney said. “It is happening with the Labor Relations Board.”

It was an unusually pointed and personal attack on Mr. Obama, whom Mr. Romney has long sought to portray as an overzealous advocate for labor unions, and it appeared deliberately timed to appeal to Republican primary voters in South Carolina: the state has relatively relaxed union rules and a labor board decision involving a Boeing airline plant there has stirred widespread anger.

Senator John McCain, campaigning with Mr. Romney, offered an equally stinging broadside of the appointments, which were made by Mr. Obama on Wednesday. “This is a classic example of the way this president regards, and frankly abuses, the office of the presidency of the United States,” Mr. McCain said.

On Wednesday morning, Mr. Romney released a new campaign commercial in South Carolina that called the board’s opposition to building the Boeing plant in the state “un-American.”

In the past, Mr. Romney has directed his campaign attacks on the labor board itself, calling its appointees “union stooges.”

At a Boys and Girls Club in Salem this morning, he focused on Mr. Obama himself, saying the president’s appointments to the board amounted to “paying back the big unions” for their endorsement in 2008.

“This president is a crony capitalist,” Mr. Romney said. “He is a job killer.”

The president’s relationship with organized labor has become the focus of Mr. Romney’s central critique of the Obama presidency: that it promotes an “entitlement society” driven by government spending and judgments, rather than the rules of the free market.

“You know he said he wanted to create green jobs,” Mr. Romney said of the president. “I don’t think we understood that he wants to give jobs to the people who gave him the green.”