If the rents don't go up, the public utilities bill don't go up (Water, Electricity, Gas), and the overall commodities don't go up, why would the hawkers raise prices to undermine their market size?
so, I do agree with uncleyap... this is downright forced extortion...
How about asking them the hawkers not to raise price for 6 months, at the same time, give them special rebates / discounted rents, PUB bills for 6 months? In this case it'll be fairer...
asking the hawkers to not to raise price is equivalent of them absorbing the higher cost of rent, PUB bills, and commodities increased cost... it is rather unfair don't you think?