The provincial agency building the $8.4-billion Eglinton light-rail line is seeking clarity from the city as Mayor Rob Ford and some councillors argue over whether it should be entirely underground.

"In order to continue with this important project we require the support of, and clarity from, the City of Toronto," Metrolinx chair Robert Prichard wrote in a letter dated Tuesday and addressed to Ford and Coun. Karen Stintz, who is the Toronto Transit Commission chair.

Stintz and other councillors say they do not want the entire line underground, but the mayor insists he wants the route buried.

Originally, the plan was to have the Eglinton LRT only partially buried. But that changed when Ford took office and struck a deal with the province to put it fully underground.

Stintz has said that going back to the original plan could cut the Eglinton LRT price tag by $1 billion — money that could be used on other transit projects.

People opposing the mayor's plan got a boost this week when Coun. Joe Mihevc received a legal opinion stating that Ford didn't have the power to make alternative transportation plans without consulting council.

In the letter, Prichard wrote he's concerned that the memorandum of understanding hasn't been approved by council. "Absent council's endorsement of the MoU, the City is not bound by the plan and it is increasingly difficult for Metrolinx to implement it."

With files from The Canadian Press