Gov. Scott Walker has rejected the heart of a GOP roads plan, saying it amounted to a net tax increase on fuel of more than $400 million over two years.

Assembly Republicans put forward the proposal Thursday to apply new taxes on fuel, cut the state's required markup on gas and dramatically scale back income taxes over the next 12 years.

In a phone interview late Friday, the GOP governor made clear he's unwilling to drop his pledge not to raise gas taxes.

"So if people are buying fuel for their vehicles, their cars and trucks, that is a net tax increase of $433 million, which obviously to me is problematic," Walker told the Milwaukee Journal Sentinel.

Walker cautioned he was still reviewing the transportation and tax plan but still raised several other concerns about the proposal's key parts.