Outside interest groups are already picking sides in Virginia's governor race and lining the pockets of Democrat Terry McAuliffe and Republican Ken Cuccinelli with plenty of cash to help win what is shaping up to be one of the state's most costly elections.

There are no limits on how much money a candidate can accept in Virginia, meaning individuals, political action committees, unions or corporations can donate unconditionally. That could open up the floodgates as national and state organizations and businesses wade into the country's marquee political contest this year.

McAuliffe received $5.1 million in campaign contributions in the first three months of the year, more than double the $2.4 million raised by Cuccinelli, who as a top state official wasn't allowed to raise cash while the General Assembly was in session during that time.

One in every 10 dollars raised by McAuliffe between January and March came from labor unions, including $100,000 contributions each from the American Federation of State, County and Municipal Employees, the American Federation of Teachers and the International Association of Fire Fighters.

Organized labor has a small presence in Virginia, a state with strong right-to-work laws. McAuliffe supports the state's anti-union law, but labor groups are sticking with him out of concern that, as governor, Cuccinelli would further curb union representation and public employee benefits.

"We are hoping that Gov. McAuliffe would work with us to repair some of the things [Republicans have] done and advance legislation to protect the health, safety and financial interest of our members," said Mike Moehler, president of Virginia Professional Fire Fighters.

Meanwhile, Cuccinelli got a $1 million boost from the Republican Governors Association and raised another $1.4 million on his own. Energy companies and their executives gave more than $150,000 to Cuccinelli, who as attorney general waged legal battles against the Environmental Protection Agency and climate-change science and accused President Obama of waging a "war on coal," an industry vital to the economy of Southwest Virginia.

Murray Energy Corp. gave Cuccinelli $50,000, while Consol Energy Inc., Koch Industries and Dominion Resources all chipped in $25,000 apiece.

Dominion, a frequent donor to both political parties, also gave McAuliffe $20,500. McAuliffe, who has touted green technology's potential, received $50,000 from the Virginia League of Conservation Voters, an environmentalist group.

Cuccinelli also received a boost from anti-abortion groups. The pro-life Campaign for Working Families gave Cuccinelli $10,000, and Wyoming billionaire Foster Friess, a well-known backer of Christian conservatives, gave the attorney general $25,000.

The Cuccinelli and McAuliffe campaigns chose not to comment on fundraising Tuesday, a day after the deadly bombings in Boston and the day of the six-year commemoration of the Virginia Tech massacre.

Bob Holsworth, a longtime political observer in the state, said the latest money war was escalating quickly. Both Cuccinelli and McAuliffe have raised more than either of the 2009 gubernatorial candidates did during the same period.

McAuliffe is "bringing in a ton of money," Holsworth said. "Cuccinelli and Republicans will have to find ways to funnel in money to remain competitive and not get overwhelmed."