(Adds comment from Potash Corp spokesman)
WINNIPEG, Manitoba, Sept 2 (Reuters) - Potash Corp of Saskatchewan (POT.TO) has warned North American customers that a strike at three of its mines may affect deliveries, an analyst at JP Morgan said in an alert to clients on Tuesday.
Analyst David Silver said fertilizer consultancy British Sulphur has reported that Potash Corp told its domestic customers that the strike, which began Aug. 7, will affect delivery schedules.
"Global potash markets are already exceptionally tight, and the strike further limits supply," Silver said.
A spokesman for Potash Corp declined to comment directly on the report, saying the company is discussing its contractual obligations with customers.
"We view our obligations to our customers, both domestic and international, as proprietary, and at this point, we're not discussing them publicly," Bill Johnson said.
Potash Corp shares were down 4 percent at C$177.50 on the Toronto Stock Exchange amid a broad downturn in commodities.
About 500 workers represented by the United Steelworkers union are on strike at three of the company's mines, which account for about 30 percent of Potash Corp production and about 6 percent of world supplies.
There were no talks scheduled, Johnson said.
The company has said the strike has affected industrial customers, accounting for about 5 percent of sales.
"As far as the rest of our customers are concerned, it remains early days in this strike, and we're still assessing the impact it will have on the ability to meet our commitments in the original timeframe," Johnson said.
The strike started during a seasonal lull in fertilizer shipments, but analysts have said it could boost world prices if it lasts past mid-September, when demand picks up.
"As (the strike) goes on, it will certainly remove some supply from the system," Johnson said. "It's a tight market."
Potash Corp restarted the largest of the three mines last week, but has not said how much volume it hoped to produce.
Analyst Silver said the company could restore about half the Allan mine's production, but unless the strike ends, it may soon have to declare force majeure on contracts it can't fill.
$1=$1.07 Canadian Reporting by Roberta Rampton; editing by Rob Wilson