The move comes as Senate negotiators work to hammer out a consensus that would include such a measure in the body's package of gun reform legislation.
The group, chaired by Boston Mayor Thomas Menino and New York City Mayor Michael Bloomberg, surveyed likely voters in 60 states and congressional districts.
In Pennsylvania, the survey found 88 percent of likely voters support universal background checks, while 90 percent of voters in Lehigh Valley Congressman Charlie Dent's 15th District support subjecting all gun purchases to background checks.
The statewide results mirror those in a Morning Call/Muhlenberg College poll released last month.
The group also surveyed voters in Pennsylvania's moderate and suburban 6th, 7th and 8th districts, finding similar sentiments.
But the poll also said just 3 percent of 15th district voters consider fixing gun laws one of their two most important issues when they head to the polls in 2014. The economy and the federal budget deficit topped the list.
Expanding the screenings to include all sales, including sales at gun shows and between private individuals is considered one of the most likely gun control measures to pass in the wake of the shootings at Sandy Hook Elementary School in Newtown, Conn.
It has been a centerpiece of President Obama's gun control efforts.
Dent has signalled that he could support some enhancements to background checks, but has not come out in support of imposing them on all gun sales.
The Mayors Against Illegal Guns poll, conducted from Feb. 1 to Feb. 5 in the 15th Congressional District, surveyed 400 likely voters. It has a margin of error of +/- 5 percent.