We are a small towing and auto repair, and storage facility. Our taxes and rent has gone up over the years. We need to raise our storage rates for a company that stores over 80 vehicles with us. For the past 3 years we have not only stored vehicles for them but we have done a lot of clerical work for them and other duties as well which has not been included with the storage price. We love this company and think their great but doing these other duties for them have taken productivity away from our main business and we need to be compensated for our time. We need to know how in a nice way to inform them that we have not raised their rates in 3 years that it is going up. We can't afford to lose them but we can't afford to keep them either. Help

You might try a Praise Sandwich (praise-hard news-praise), as in the following example:

"We've appreciated your business over the past three years and have enjoyed working with you as a customer. Our business relationship has been enjoyable for us, and we've always tried to go that extra mile to show our appreciation. That's included trying to keep our rates low for excellent customers like yourself. Unfortunately, our overhead including taxes and rent have been going up over the past few years in this difficult economy, and we're forced as a result to raise our storage rates. Please see the attached revised rate sheet for details, and let us know if you have any questions. We do truly enjoy serving you, and if there's any way we can enhance our services to improve your satisfaction with our services let us know. We're looking forward to another three great years together!"

That of course is just an example. You want to avoid any mention of the hardships this relationship has placed on you, since that would likely come across as complaining.

Vasily