If the working hours would be reduced from 40 hours / week to 32 hours / week (4 days x 8 hours instead of 5 days x 8 hours), but maintaining the wages at the same levels, then I guess that the price of the commodities would increase.
If, for example, I am producing clothes with 10 workers, each producing 100 shirts per week (20 per day) and I sell the shirts for \$1 each, then I make \$1,000 per week, covering the production costs. Reducing the working hours from 40 to 32 / week means I can produce only 800 shirts per week (200 shirts per day x 4 days) but since I need \$1,000 per week in order to cover the costs, that means I have to sell the shirts for \$1.25 (that comes from dividing $1,000 to 800 shirts)
Therefore, at a first sight, it looks like reducing the working week to four days implies a 25% increase for the prices of the commodities.
Am I right?