I worked for a comany when I first started out that did something similar. It was 20% on service work and 10% on installations. It sounds ok at first, but then during inventory time the boss expected us to inventory for free, no hourly wage for non-billable time. They were constantly mandating us to come in for this or that, but no pay since it wasn't billable. My wife ended up researching this on the web and found it to be il-legal completely in Illinois. We submitted a request for missed wages and were laughed at. My wife was mad, called the department of labor. Since the boss didn't even meet minimum wage when the pay versus hours were figured his but was in a sling. He then began jockeying his bussiness classification around to be classified as a sales bussiness, like a realtor, instead of a service company, like an hvac contractor. Then he realy screwed himself, he got out of having to pay back pay to any of us, but he got raked over the coals by state and federal government for not paying his taxes like a sales shop. It cost more than if he had just paid us for non-billable time he mandated us to work.