Ainsworth Game Technology’s second-largest shareholder has accused the poker machine manufacturing group of undervaluing its American property assets by more than 40 per cent in an escalation of a terse dispute between investors about whether to sell the business for $337 million.

Austrian gaming giant Novomatic is the largest shareholder in Ainsworth and made an offer to buy the 47.1 per cent of the business it did not own for $1 per share in April. The offer has outraged other shareholders, including heavyweight investors Allan Gray, Spheria Asset Management and Kanen Wealth Management, who think the deal undervalues the business.