Wal-Mart is expected to fight a Canadian labour board decision to accredit a trade union in a store in the Eastern province of Quebec.
Consumers like the low prices but workers say low wages hurt
The Quebec Labour Relations board gave the go-ahead for union representation at the Saguenay store late on Monday.
If the decision is upheld, it could be the first time Wal-Mart will have a unionised workforce in North America.
The retail giant has successfully fought earlier attempts to establish unions in its Canadian stores.
Wal-Mart, the world's largest company in terms of revenues and employees, has profited from its strategy of low prices. This has, however, resulted in lower salaries for its non-unionised workforce.
Wal-Mart previously successfully contested a ruling by the Saskatchewan Labour Relations Board, which had approved the establishment of a union.
But labour codes in Canada vary from province to province, and union representatives argue that the Quebec labour law is among the toughest in North America.
"They are going to try many different legal procedures to avoid this but the law is very clear," Louis Bolduc, Quebec Canadian director for the United Food and Commercial Workers Union told BBC News Online.
The Wal-Mart sign is familiar to shoppers in North America
"I don't think they will succeed in Quebec...They will have to sit and negotiate a contract."
The Quebec Labour Relations board accredited the union because the required majority of staff wanted to be represented in that way, Mr Bolduc said.
In other provinces, the company can request a vote to be held at a later date.
According to Mr Bolduc, high staff turnover in service industries can effectively weight the vote in the company's favour.
The Quebec Labour Relations board is to meet on 20 August to outline the scope of the union bargaining unit for the Wal-Mart workers.
Repeated attempts to contact Wal-Mart, both in the US and Canada, were unsuccessful.