The Canadian government is urging the Obama administration to pay for its share of the costs for building a customs plaza on the U.S. side of a planned bridge linking Detroit and Windsor, says Transport Minister Lisa Raitt.

Canada has been working under the assumption the U.S. would pay $250 million to build the customs plaza, a key link to the Detroit-Windsor bridge, but a lack of money allocated in the U.S. federal budget in March has sent a signal that funding for the project could be at risk.

NDP MP Brian Masse, during question period in Ottawa on Tuesday, accused the federal government of dropping the ball by failing to secure funding for a project the government has described as "Canada's top infrastructure priority."

"Could the minister assure Canadians that they will not be on the hook or front the money for the cost of building the U.S. government's customs plaza in Detroit," Masse said.

'We are committed to paying its fair share and we expect, as well too, that the U.S. pay and be responsible for its share.'— Transport Minister Lisa Raitt

While Raitt did not rule out the option, she did say that Canada will continue to urge the U.S. government to fund its share of the border inspection plaza.

"We are committed to paying its fair share and we expect, as well too, that the United States pay and be responsible for its share," Raitt said during question period on Tuesday.

"But we will continue to talk with our partners in the U.S. and we will continue to work on this bridge," Raitt said.

Canada has pledged to pay $1 billion for the bridge linking Detroit and Windsor, which is expected to open in 2020. Last month, Ottawa budgeted $630 million for the construction of the bridge.

In a telephone interview with CBC News on Wednesday, Masse said he hand-delivered a three-page letter to Raitt, following Tuesday's question period, expressing a number of concerns over the level of uncertainty surrounding the funding for the U.S. plaza.

In the letter, Masse points to a section of the Crossing Agreement dated June 15, 2012, that would leave Canada responsible for financing the customs plaza unless "U.S. federal agencies agree" to take on the responsibility.

"What if the appropriate U.S. federal agencies do not agree?" said Masse in his letter to Raitt.

"Canadians need to be reassured that public resources are being allocated responsibly."

CBC News asked Raitt's office at what point Canada would become responsible for the financing of the U.S. federal plaza if the U.S. doesn't live up to its financing commitment.

A response from her office said Canada has budgeted for its share of the project, but did not address how the Canadian government would budget for a possible $250 million shortfall.

Raitt has described the Windsor-Detroit bridge project as "an incredibly ambitious and bold project" that would "help create jobs."

Mobile users, read the NDP letter to Lisa Raitt here