Thursday’s crowd was particularly receptive as Mr. Romney said he would pursue right-to-work laws and forbid unions from collecting dues that could be used for political purposes.

“If I become president of the United States, I will curb the practice we have in this country of giving union bosses an unfair advantage in contracting,” Mr. Romney said. “One of the first things that I will do – actually on Day One- is I will end the government’s favoritism towards unions in contracting on federal projects.” The audience responded with a standing ovation.