Tips for writing an effective letter
Be polite
You don't listen to someone who is rude to you or attacks you, neither will the person you are writing to. Be professional and courteous, to encourage your audience to keep reading.
Target your content to your reader
When writing to the Minister for Agriculture, explain how this rule is impacting your farming. When writing to the Minister for Finance, show how this is hurting your farm' s profitability (and therefor taxability). A municipal official might be more interested in how you see this as undermining municipal authority. When writing to the Premier, consider bringing up how a Crown Corporation is working against Manitobans, and so on.
Avoid heresy
Stick to the facts. Don't write about something you heard from the neighbor of your cousin's brother-in-law. Only describe the impact of this unfair rule when you know it to be true.
Be firm
When writing public officials, it is your right to (politely) state that you expect them to do something about this.
Be professional
Use spellcheck. Sending a letter full of spelling and grammatical errors suggests you don't care much. If you don't, why should the person you are writing to? If you are a poor speller, consider getting someone to proofread your letter.