Asda is to take legal action in a bid to prevent a proposed five-day strike by thousands of workers at its distribution depots around the UK.
Asda says there were "serious irregularities" in the strike ballot
Members of the GMB union are due to walk out next Friday after staff backed action in a ballot.
However, the supermarket giant says it plans to seek an injunction against the strike because of what it calls "serious irregularities" in the ballot.
The dispute centres on pay, health and safety and national bargaining.
"There were serious flaws in the ballot process with people who don't even work for Asda being sent ballot papers," said Asda's People Director David Smith.
"We have tried raising this with the union but they have ignored us.
"With only 1% of our colleagues voting for a strike, we've got to do all we can to protect the other 99%."
A GMB spokeswoman said it was taking legal advice and would make no immediate comment.
World Cup effect
The five-day strike is due to begin from Friday, 30 June, which is the start of the quarter final stage of the World Cup.
If the England team make it through to that stage, and the strike goes ahead, it would hit Asda at a very busy time, with football fans aiming to stock up on food and drink.
Asda, which is owned by US retail giant Wal-Mart, has already vowed to keep any disruption to a minimum if the strike does go ahead.
The walkout is planned to take place at the supermarket's 20 distribution depots around the UK after almost three quarters of those who voted in the ballot backed the industrial action.
Disputed union numbers
The strike action is linked to the GMB's dispute with Asda over the company's refusal to allow it to negotiate nationally for its staff at all Asda depots, which in turn relies on how many members are in the union.
Asda and the GMB dispute how many of the supermarket's 12,500 UK depot workers belong to the union.
The union says the figure is 7,000, but Asda says the number is nearer 4,500.
The two sides also disagree about profit-related bonus pay.
Asda's depot sites include Bedford, Chepstow, Dartford, Didcot, Erith, Falkirk, Grangemouth, Ince George in Wigan, Lymedale Staffordshire, Lutterworth in Leicestershire, Portbury in Bristol, Skelmersdale, Teesport, Wakefield, and Washington.
The GMB said it could take legal action against any employment agency which supplies staff to Leeds-based Asda during the strike.