MICHIGAN CITY, Ind. — Competition from a tribal casino that opened this summer in southwestern Michigan has led Blue Chip Casino to lay off employees, a spokesman said.

Blue Chip, on Lake Michigan, began laying off 6 percent of its workforce Friday, said David Strow, a spokesman for parent company Boyd Gaming.

Strow attributed the layoffs to competition from the Four Winds Casino about 10 miles away in New Buffalo, Mich., which opened in August.

Blue Chip increased marketing efforts to limit the impact of the new casino on attendance and revenues, Strow said. But attendance in August was down by about 54,000 and revenues were down by about $5.5 million compared to the previous month.

“This was a last resort,” Strow said. “This was a very difficult decision.”

Strow did not say how many employees were affected, but Michigan City Mayor Chuck Oberlie said the casino employs about 1,100, which would put the number laid off at between 60 and 70.

“I don’t know that it was totally unforeseen,” Oberlie said Friday. “With the Four Winds, a small adjustment could be expected.”

Strow said employees who are laid off would be given first preference when hiring begins next year for the casino’s new 22-story hotel, part of a $130 million expansion.

“We’re obviously aware of the impact to employees, and we will take steps to assist them,” he said. Of the casino’s future, Strow said: “We’re still very optimistic for the prospects long term at Blue Chip.”