"The Supreme Court is abundantly clear about the limits of the governor’s line-item veto authority and there is no doubt Governor McAuliffe exceeded that authority in these two instances," Howell said in a statement today. "The legislative branch cannot acquiesce to this expansion of executive authority."

McAuliffe spokesman Brian Coy said the governor would review Nardo's decision, but he added, "It is worth noting that is a clear example of the General Assembly being unable to accomplish something through legislation and resorting to legislating through the budget."

McAuliffe also has attempted to use the budget to expand Medicaid, but Nardo's decision not to recognize the governor's veto of the condition on public-private transportation projects came as something of a surprise. The governor also had vetoed related appropriations, including a commitment to Washington Dulles International Airport, and directed his transportation secretary to work around them.

The vetoed budget item extends a prohibition on requiring public labor agreements with unions to public-private transportation deals, as the state already forbids for conventional projects managed by the Virginia Department of Transportation. The budget language made an exception for projects crossing state lines, specifically Maryland, which generally requires project labor agreements.