OTTAWA, Aug 19 (Reuters) - The Canadian government,

trying to head off a crippling transport stoppage, on Monday

told the country's two main railway companies and the Teamsters

union to work harder to reach labor deals.

Unless agreements are reached, both Canadian National

Railway ( CNI ) and Canadian Pacific Kansas City ( CP ) will shut down at the

same time early on Thursday for the first time in history.

Canada - the world's second-largest country by territory -

relies heavily on rail to ship grain, fertilizer and

commodities, and the country's main business lobby group

estimates losses would hit C$1 billion ($733 million) a day

during a stoppage.

Federal mediators are working with the companies and the

union, but those involved in the discussion say little progress

has been made. The union says CN Rail and CPKC want to dilute

safety provisions, a charge the companies deny.

In a post on the X social network, federal Labour

Minister Steve MacKinnon said the effects of the talks would be

borne by all Canadians.

"The parties must do the hard work necessary to reach

agreements at the bargaining table and prevent a full work

stoppage," he said.

MacKinnon has the power to force the union and railway

companies into binding arbitration, but has so far said he wants

them to sort out their differences at the negotiating table.

Labor talks started early this year but progress has

been slow, with both the union and the companies accusing each

other of bad faith.

CN Rail and CPKC have already stopped accepting shipments of

hazardous goods and are winding down their operations.

Maersk said on Monday it would stop accepting some

Canada-bound shipments.

Canada is a major agricultural producer, and farmers

will start bringing in their harvests in August and September.

The Quorum Corporation, which monitors grain handling

and transportation, said daily volumes in early September would

increase to 138,000 tonnes with a value of around C$75 million.

"After a period of time, sales will be lost and the

value of Canada's grain will decrease ... the largest concern is

a further degradation of Canada's reliability as a supplier,

which is already suffering due to past labor disruptions,"

Quorum President Mark Hemmes said in an emailed statement.

Concerns are rising that container shipments coming into

and departing Pacific Northwest ports and Canadian Pacific ports

will be halted as port workers' unions have indicated they would

not handle cargo slated for the Canadian railroads.

Refrigerated containers with meat and some highly

perishable produce are of particular concern because delays

would likely mean spoilage.

Shippers of those goods have started holding back

containers, said Peter Friedmann, executive director of the

Agriculture Transportation Coalition.

($1 = 1.3641 Canadian dollars)

(Additional reporting by Karl Plume in Chicago and Abhijith

Ganapavaram and Abhinav Parmar in Bengaluru:

Editing by Franklin Paul and Paul Simao)