A conspicuous blue hybrid big-rig/pickup truck has become a surprising icon for Republican Terri Lynn Land’s Senate campaign in Michigan.

It looms over campaign events. Land rode on it during a Fourth of July parade. It even has its own Instagram account.

But the gimmick on wheels could potentially become a political liability for Land, who faces a competitive race against Democratic Rep. Gary Peters.

Land’s campaign rents the truck — in fact, two identical ones, as a Michigan blogger disclosed this week — from her brother-in-law Roger Lucas, at a cost of $1,000 per month, according to the most recent Federal Election Commission filings.

That’s roughly $17 per day per truck, a price Democrats say is below fair market value and potentially in violation of campaign finance rules.

Land “is already potentially breaking the law to funnel millions of her family's wealth to her campaign, so it's clear she doesn't think the rules apply to her. Now, she is trying to cheat campaign laws again by not paying fair market value for her two campaign trucks,” said Kevin McAlister, a spokesman for the Michigan Democratic Party.

But Land’s campaign says the truck, which appears to be an International CXT, is more than 10 years old and not in excellent condition, reducing its value. The campaign would not disclose the truck’s make and model.

“The Land campaign has consistently paid fair market value for use of this almost decade-old truck,” said Land spokeswoman Heather Swift. “The monthly payments have, and will, cover usage of the truck from September 2013 through November 2014. Use of the truck was minimal in 2013 and will increase through Election Day, and rental payments properly reflect that valuation.”

Similar trucks are listed for sale online for approximately $75,000 to $85,000.

The brewing controversy brings to mind a similar brouhaha in Kentucky, where Democrat Alison Lundergan Grimes has denied receiving a family discount from her father’s company for her campaign’s bus, which Republicans charge is being rented at less than fair market value. In that case, the Democratic Senatorial Campaign Committee has been dismissive.

Land is renting directly from a family member, not from any corporation — which means the trucks are considered in-kind donations to the campaign. When the rental value exceeds individual contribution limits, it could be a campaign finance violation.

However, market value can be ambiguous unless formally challenged by another campaign or party.

"For most things you look at fair market value,” said Larry Noble, former FEC general counsel now with the Campaign Legal Center. “If you're going to rent the campaign a car, look at what campaign would have to pay at arm's length for that car.”

Land has already taken some heat in this election over other financial issues, including her stake in her family’s business, Land & Co. Land initially released her tax returns without her husband’s, which were filed separately and showed the wealth they had amassed through the company, drawing criticism from Democrats.