A new poll finds the mayor's push to bring congestion pricing to the city has seen a decline in support from New Yorkers over the summer.According to the latest Quinnipiac poll released Thursday, 57 percent of New Yorkers oppose the plan to charge drivers south of 86th Street in Manhattan.That's 5 percentage points higher than the number of people who opposed the plan in a Quinnipiac poll taken in July.However, the poll also found that 89 percent of voters say traffic congestion in Manhattan is either a very serious, or somewhat serious problem.Manhattanites remain the only ones in favor of the plan, which calls for charging cars $8, and trucks $21 for entering or leaving midtown Manhattan during peak hours.Bronx residents, with 74 percent, were the most likely to oppose the idea.However, an environmental group raised serious questions about those poll findings.Transportation Alternatives accuses the Quinnipiac poll questions of being misleading and biased. The group says the questions gave the impression that congestion pricing fees would be charged throughout the entire day -- instead of the times between 6 a.m. to 6 p.m.It also says pollsters did not let people know that Mayor Michael Bloomberg's plan would be a trial program.Transportation Alternatives says, the more city residents know about the benefits of the plan, the more likely they would be willing to support it.Quinnipiac surveyed nearly 1,200 registered voters in New York City last week. It has a margin of error of plus or minus 2.8 percentage points.