Democrat Jason Crow hit the airwaves with his first TV ad Monday in the race for Colorado’s battleground 6th Congressional District.

“When you see injustice, you have to lead by example, so I’ve taken a pledge that I’m not going to take a dime of corporate PAC money,” Crow says in the 30-second spot, airing on broadcast stations and cable channels in the suburban district.

The ad highlights the first-time candidate’s experience in the Army, which included three combat tours with both conventional and special forces in Iraq and Afghanistan and receipt of a Bronze Star.

Crow, a partner at a leading Colorado law firm, is facing clean energy expert and author Levi Tillemann in a vigorous primary for the chance to challenge Republican U.S. Rep. Mike Coffman, an Army and Marine Corps veteran seeking his sixth term.

Voters start receiving mail ballots next week, and they’re due back to county clerks by June 26.

According to a general election poll conducted in February, the district’s voters favor Crow by a 10-point margin over Coffman after learning the Democrat is rejecting contributions from corporate PACs. The survey, commissioned by End Citizens United, a liberal group that backs campaign finance reform and had earlier endorsed Crow, didn’t measure Coffman against any other challenger.

The district, one of just two dozen nationwide won by Democrat Hillary Clinton but held by a Republican, is among the Democrats’ top targets in the midterm elections.

It’s already shaping up to be the state’s most expensive congressional contest.

Last month, a Republican super PAC reserved $2.3 million worth of fall TV advertising to defend Coffman as part of its initial nationwide ad buy. The Congressional Leadership PAC also plans to spend heavily on digital advertising in the district and fund field operations in key districts.

The House Majority PAC, a Democratic super PAC, said in March it would book $1.76 million in TV ad buys in the Denver market. The sum could also include spending aimed at U.S. Rep. Scott Tipton, a four-term Republican representing the 3rd Congressional District and another Democratic target.

A spokeswoman for Crow wouldn’t say how much the campaign is spending on the TV buy. According to figures provided to Colorado Politics by a media analyst, the campaign spent roughly $50,000 for the first week of its cable buy – a substantial amount for a congressional race.

Watch the ad here: