By Steve Tawa

PHILADELPHIA (CBS) – Mayor Nutter, along with more than 20 Mayors from around the country, have signed a strongly worded letter to Republican presidential candidate Mitt Romey, in hopes of getting him to release more tax returns.

This was done after a get-together in Philadelphia this past week, in their effort to get Congress to invest more in cities.

As president of the U.S. Conference of Mayors, Nutter emphasized bi-partisan support to increase spending on the country’s infrastructure. After that event was over, in the hallway of a center city hotel, Mayor Nutter read the letter aloud.

“Without releasing additional tax returns, you would go down as one of the most secretitive presidential nominees in modern history. Even Richard Nixon released more years of tax returns than you.”

Then Nutter was asked whether taking a political shot at Romney undermined their non-partisan call on the government to invest in cities.

“In our individual capacities, we always reserve our right to be actively engaged in the political process. i expect that some of my fellow republican mayors may be actively engaged, and theyr’e going to do their thing as well.”

Mayor Nutter also pointed out President Obama released 12 years of tax returns, and other presidential candidates, including Romney’s father, advocated the public release of several years of tax returns.