Brokers' postage bills could more than double as the Post Office implements radical changes to mail charges.
Several brokers have told staff to keep post to a minimum, with some even removing branding from letters to maintain low costs.
Broker Network said it sends out, on average, 200 policy documents weekly. "This used to cost between 23p and £1 [per document], but now it has gone up to a starting point of 75p up to £2.50," a spokesman said.
A north London broker said the changes to postal charges, which were brought in on Monday, are likely to increase its postal expenses by around £1,200 a year.
He said: "We spend about £250 a month on postage. I would expect the amount we spend each month to go up to nearer £350 as we send out all of our post first class. That is a bit of a chunk out of our income."
Peter Staddon, Biba's head of technical services, said: "It's going to be a nightmare and I'm sure this hasn't been done to make the Post Office more efficient.
"It's going to be a tough time but brokers can find dramatic solutions and I hope that this comes back on the Post Office."
Under the new system the price of postage will be based on the size of the package as well as the weight.