One of the biggest rip-offs the U.S. government enforces is a ban on cheap pharmaceutical drugs from Canada. Americans are barred from buying perfectly safe pharmaceutical drugs from Canada that can be 20 to 80 percent cheaper than American drugs.

Conservative organizations like the Cato Institute and progressive lawmakers like former Senator Byron Dorgan (D-ND) have long advocated for ending this ban and having free trade in pharmaceutical drugs. It would mean cheaper drugs for Americans and more funding for drugmakers and a health care system that can better regulate costs.

But the American pharmaceutical industry is incredibly powerful, and uses its political clout to continue this effective embargo.

Which brings me to the Montana Senate race. A group calling itself Citizens for Strength and Security (CSS) has been running television advertisements against Rep. Denny Rehberg (R), the Republican candidate for U.S. Senate. View one of them above. It attacks Rehberg for voting for congressional pay raises. What the ad does not openly tell you is who funds CSS.

Many of the group’s funders are fairly typical Democratic Party interest groups that are more loyal to his opponent, Senator Jon Tester (D), like the American Federation of Teachers and the Service Employees International Union.

Interestingly, Pharmaceutical Research and Manufacturers of America (PhRMA), the drug industry’s trade group, gave enormous contributions to the group in 2010, according to tax filings with the IRS. It gave $2.5 million to CSS’s Action Fund and $875,000 to the group itself.

What is PhRMA’s interest in sinking Rehberg? In 2003, the congressman voted to end the prohibition on Canadian drugs. Meanwhile, Tester voted against drug reimportation when it came up as an amendment during the health care reform debate. In 2011, he did, however, push for a bill that would allow for the reimportation of foreign material — antique guns, to be exact.

Paying back Tester while rebuking Rehberg appears to be a likely motivation for PhRMA’s support for CSS as it seeks to intervene in the Montana race.

Whoever wins the race, chances are that the drug industry will continue to spend big to make sure Americans can’t buy cheaper Canadian drugs with their own money.