The latest TV ad by Mayors Against Illegal Guns, the gun control group funded by Mayor Mike Bloomberg, hit the airwaves in Nevada this week, ahead of a close vote Wednesday on a background check bill that passed the state Senate.

The bill would close the loophole that allows private sales to be made without checking the criminal background of the purchaser. It also bans people deemed mentally ill and likely to harm someone from possessing a gun. The bill can be followed on Scout, Sunlight's tool for tracking the progress of state and federal legislation.

The bill passed the Democrat-controlled state Senate by one vote, along party lines. It still requires approval by the Democrat-controlled Assembly and Republican Gov. Brian Sandoval, who said he has not decided whether he will back the bill or not.

The ads ran Tuesday and Wednesday on at least two channels — the Las Vegas FOX and CBS affiliates. The group paid a total of $2,600 to run four 30-second ads during the evening news on the channels, according to Political Ad Sleuth, Sunlight's tool for tracking political ad purchases. The new ad appeared on Ad Hawk, Sunlight's tool for tracking TV ads.

The ad also ran in Reno, according to Erika Soto Lamb, communications director for Mayors Against Illegal Guns.

The only ad purchases that are posted to the Internet in Nevada come from the Las Vegas market, which does not cover the whole state, and only from the four biggest local TV stations there, according to a rule enacted by the Federal Communications Commission to increase transparency of political ads last year.

The National Rifle Association is against the Nevada legislation, which it called an "extremist anti-gun bill" in a blog post asking supporters to call their state senator to oppose it. 

The bill would create a "huge burden for law-abiding citizens," according to the NRA, which also claims "it paves the way for universal background checks."

Both the NRA and the Mayors Agaisnt Illegal Guns employ lobbyists to push their causes in the Silver State legislature. The Mayors are represented by two firms and 11 lobbyists while the NRA has one in-house lobbyist working in Nevada, according to state records.

Like many ads run by the Mayors, the Nevada spot used an emotional plea from a family member of a victim of the massacre that killed 26 people in Newtown, Conn., late last year. It asks viewers to call their state senator to support SB 221.

The group also ran a slew of ads to push for federal gun control legislation, which failed in April when it did not get the 60 votes required in the Senate to overcome a filibuster. Since then, it has run ads criticizing senators such as Kelly Ayotte, R-N.H. and Jeff Flake, R-Ariz., for voting against the background check bill.