DETROIT, Mich -

Vice President Joe Biden had a strong message to unionized workers in Detroit today -- he and the president have their backs.

During the annual Metro Detoit Labor Day rally, Biden described President Barack Obama's re-election campaign as a battle to protect and defend the interest of the working class. He urged the crowd to step back and take a critical look at Republican presidential nominee Mitt Romney and running mate Paul Ryan.

Biden said Romney and Ryan don't fully appreciate the role union workers have played in building the country.

This campaign push comes as Democrats prepare for the Democratic National Convention, slated to begin Tuesday in Charlotte, N.C., where the party will nominate the Obama-Biden team for a second term.

Union leaders have been upset with the choice to hold the convention in Charlotte because they have noted it doesn't have any unionized hotels.

President Obama also spoke today in Toledo, Ohio.