Which middle class tax hikes have been proposed? President Obama is using a "study" which claims that to fulfill all his campaign promises, Romney will have to

Which middle class tax hikes have been proposed? President Obama is using a "study" which claims that to fulfill all his campaign promises, Romney will have to raise middle class taxes, but that's not the same thing. It would be as if I'd claimed in 2008 that Obama would have to raise middle class taxes to fulfill his pledge to cut the deficit in half by the end of his first term. What happened with that, anyway?