Chris Roan, prosecuting for Cambridgeshire Trading Standards, said Brian Sharpe's Cambridge-based company, Abcam, had falsely advertised membership of the FMB in two editions of the Cambridge Yellow Pages.
Roan told magistrates that Sharpe had tried to gain an unfair advantage over other builders and attempted to gain customer confidence by claiming membership of the FMB.
FMB eastern regional director Steve Bowen said: "I am pleased that it came to court because this builder was openly flaunting it. But I am sad the fine wasn't higher, because people make a lot more money than that out of false claims."
Bowen said that the public should be more vigilant when choosing builders. "There are too many cowboys out there. But we need to educate the public as well, because people will always be looking for champagne on beer money."
The FMB attacked Gordon Brown's budget this week.
Director-general Ian Davis said: "We knew about the extra costs of fuel and road tax on vehicles which affect our members. But it was more than a little sneaky to announce swingeing increases to the landfill tax after the budget was hailed as an enterprise budget."
The FMB also criticised the decision to increase the VAT threshold to £51 000 and added that the government's Cowboy Builders Working Group was likely to recommend cuts in the VAT threshold.
National president Derrick Ovington said: "The chancellor seems to have made clear his views on these proposals before they were discussed."
He added: "Just what does the chancellor think he's doing increasing the VAT threshold when the industry wants to get rid of it and reduce the rate charged on repair and maintenance?"