NEW YORK—Mitt Romney repeated his call to curb the influence of teachers unions in public schools, arguing that the groups should no longer be allowed to contribute to political campaigns.

In an interview with NBC's Brian Williams at a network-sponsored forum on education, Romney accused teachers unions of putting their own interests above students. He said their contributions to politicians in charge of education issues are unfairly influencing the system, especially when it comes to contract negotiations.

"We have to get the money from teachers unions out of the campaigns. ... We've got to separate that," Romney said. "It's an extraordinary conflict of interest."

During a question-and-answer session at the appearance, Romney rejected the assertion of an audience member who told him polls in New York show parents back unions as organizations fighting on behalf of local students.

"I don't believe that for a minute," Romney replied, offering a quick laugh. "I know something about polls. ... And I know you can ask questions to get any answer you want."

Romney talked up his record on education when he was governor of Massachusetts, including his efforts to increase parental involvement in schools, saying it's "crucial" to a child's education. He indicated he would follow a similar path as president, calling "the home an integral part of education."

"The best teachers in the world can't overcome a home that is pulling in the complete opposite direction," Romney said.

While he dismissed Democratic charges that he would gut the education system, Romney said he would not simply throw money at problem schools, but that under his administration he would "insist that schools are graded" by their performance.

"I'm just not willing to add more spending to get people happy with me," Romney said.