A string of West End hit shows, including the Lion King, Wicked and James McAvoy's sellout performance as Macbeth, could be hit by strikes after talks broke down between the Ambassador Theatre Group and the union representing front and backstage staff.

The union Bectu, which represents theatre staff from ice cream sellers to stage hands, is balloting for strike action after talks at the conciliation service Acas over pay and conditions stalled.

A spokesman for the management said: "ATG was stunned and disappointed when Bectu decided to break off from negotiations on Monday."

Virtually all outstanding issues had been resolved, he said. "ATG is keen to continue talks with Bectu in order to find a swift resolution."

After a string of acquisitions, the Ambassadors is the largest West End theatre group and owns or operates some of the best-known stages including the Lyceum, home of the Lion King, the Victoria Apollo, where Wicked has been running for six years, the Piccadilly, where the Spice Girls musical Viva Forever is packing in the crowds, and the Donmar Warehouse, where the Oscar-winning director Joe Wright's first stage production, Trelawny of the Wells, has just opened.

In a statement, the union warned ticketgoers to check the progress of the dispute, which involves hundreds of staff most of whom are paid £6.45 an hour, just above the minimum wage.

"Plans for industrial action will not be decided until the strike ballot has got under way, but the union has already warned theatregoers that they should check in advance whether the shows they have booked might be hit."

Pat Styles, the Bectu official who has been leading negotiations, accused the group of sabotaging the talks by demanding changes in conditions agreed only a few months ago, including cutting the minimum amount of time for which front-of-house workers would be paid for each performance from 3.5 to three hours. The management spokesman said improved pay and an agreement on minimum hours had been offered at the talks and rejected.