Costco's (NASDAQ:COST) ongoing labor battle is heating up, and investors might want to buckle up. The retail giant has outright rejected a whopping 98% of the Teamsters' proposals ahead of the looming January 31 contract deadline. With 18,000 Costco workers gearing up to strike if negotiations fail, the stakes couldn't be higher. Issues like seniority protections, paid leave, and workplace surveillance safeguards are at the center of the fight, with Teamsters General President Sean M. O'Brien calling Costco's approach surface bargaining that's wasting time and treading dangerous waters.

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This isn't the Costco investors know and love. Despite raking in $6.3 billion in profits last year, the company seems to be shifting from its once pro-worker stance. Allegations of union-busting tactics, like removing union literature and locking union reps out of bulletin boards, aren't exactly a good look. Workers are demanding a contract that reflects the company's record profits, but so far, Costco is playing hardball. It is deeply disappointing that Costco has rejected or refused over 98 percent of our proposals, said Michele Javier, a Costco employee and union steward.

For investors, this could mean turbulence ahead. A strike would throw a wrench in Costco's operations, potentially impacting supply chains and sales during a critical period. With the January deadline creeping closer, the key question is whether Costco will step up to resolve this showdownor if the situation spirals into a costly labor dispute that hits its bottom line and reputation.

This article first appeared on GuruFocus.