Treasurer Jim Chalmers has slammed the Coalition’s policy to allow small businesses to tax deduct lunches with their staff and clients as unserious, as tax experts warned the measure would encourage dining out at the expense of investment.

Opposition Leader Peter Dutton courted the small business vote on Sunday by announcing that enterprises with a turnover of up to $10 million would be able to tax deduct up to $20,000 of “business-related meal and entertainment expenses” provided to clients, vendors and employees without incurring fringe benefits tax. The measure, which will last for an initial two years, excludes alcohol.