(Harrisburg) -- Environmental groups say Pennsylvania’s cities are among the country’s worst when it comes to air pollution. They’re calling on the federal government to tighten regulations. For example, Lancaster, Harrisburg and Reading are among the top smoggiest mid-size metropolitian areas. Pittsburgh and Philadelphia have some of the thickest smog of large cities in the country, according to a new report. The PennEnvironment analysis aims to convince the federal Environmental Protection Agency to get a bit more strict on how much air pollution is too much. Jeff Schmidt, of the Pennsylvania chapter of the Sierra Club, is calling for the EPA to enact strong regulations on a number of smog sources. "Coal fired power plants, industrial facilities, and internal combustion engine in vehicles," he said. "But in addition, as the Marcellus Shale drilling increases in Pennsylvania and our region, we know if they...if those sources aren’t controlled, it’ll make a bad situation worse." The state Department of Environmental Protection withdrew its support for lawsuits defending federal regulations of ozone levels. On the federal level, the Obama administration recently backed away from efforts to heighten the national standard for smog pollution. The EPA has a public hearing on the subject of gas emissions next week in Pittsburgh.