GOP presidential nominee Mitt Romney said Tuesday that contributions by teachers’ unions to the Democratic Party represent an “extraordinary conflict of interest” because many times those unions will be sitting across the table from Democratic lawmakers in negotiating their contract terms.

“I don’t mean to be terribly partisan, but I kind of am,” Romney joked to host Brian Williams in a 45-minute-long appearance at NBC’s “Education Nation” summit in New York City. “In the case of the Democratic Party, the largest contributors to the Democratic Party are the teachers’ unions.”

The most important factor in having a “productive relationship” between government and teachers’ unions, he continued, is “that the person sitting across the table from them should not have received the largest campaign contributions from the teachers’ union themselves.”

A Romney campaign spokeswoman was not immediately able to provide a figure backing up Romney’s claim that teachers’ unions represent the greatest share of donations to the Democratic Party. According to the Center for Responsive Politics, which tracks campaign contributions, the education industry is the third-largest contributor to Obama, behind retirees and those in the legal field.

Asked Tuesday whether he would allow strikes like the one in Chicago if he were president, Romney told Williams, “I don’t know that I would prevent teachers from being able to strike.”