Shares of Costco Wholesale (COST) - Get Costco Wholesale Corporation Report were lower in premarket trading on Thursday after the discount wholesale retailer giant said same-store sales in March rose 5.7%.

Costco shares were down $2.23, or just under 1%, at $243.38 in premarket trading on the Nasdaq Stock Market. They ended the trading day Thursday at $245.61.

Costco said its net sales rose 7.4% in March to $13.87 billion from a year earlier, while same-store sales rose 5.7%, or 5.9% when excluding gas prices, foreign exchange rates, and new accounting standards.

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However, this year's five-week March retail month with one extra shopping day vs. last year beefed up total and comparable sales by "one to one and one-half percent," Costco said.

Costco celebrated its strong second-quarter results last month by announcing that it was raising the wage it pays workers for a second time in less than 12 months to $15 an hour.

The company announced in June it was raising its minimum wage to $14 from $13 an hour.

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