The latest initiative by a pro-immigration reform lobbying group supported by Facebook founder Mark Zuckerberg is arousing the ire of hard-line conservatives, who are firing back online.

Last week, FWD.us launched an expensive advertising blitz against Iowa’s outspoken conservative Congressman Steve King, questioning his patriotism. One of the TV ads, which began running in Iowa this week, targeted King’s comments that undocumented immigrants who want to serve in the U.S. armed forces should instead be put on a bus “to Tijuana.”

King wasted no time responding to the ad: “I am under attack by billionaire Mark Zuckerberg because I am one of the few who will stand up and tell the truth about amnesty,” he said in a statement. “He wants amnesty because it would benefit his multi-billion dollar corporation, but I’m fighting to preserve the Rule of Law. Why would we reward people for breaking our laws? Rewarding law breakers produces more law breakers.”

And the congressman’s supporters fought back on Zuckerberg’s home turf on Facebook.

Someone going by the name Joyce Ray posted on King’s Facebook page, firing off, “Don't give up Congressman King!!! You are 100% right & those who are for Amnesty are Anti-Americans! These Illegals can NOT be rewarded for breaking our laws!!!! We need our borders sealed and properly defended & Illegals deported! It is wrong to allow them to stay & turn our great United States into the crime & mess of the countries they came from.”

Another King “friend” identifying himself as Russell Shaw and presumably speaking about billionaire Zuckerberg, said on King’s page: “Another rich arrogant selfish jerk with way, way too much money to waste!!!!!”

Earlier this month, King lashed out at the ENLIST Act proposed by Rep. Jeff Denham (R-Calif.) that would allow adults who have lived in the U.S. continuously and entered the country as children of undocumented parents, who are otherwise qualified for military service, to join the military and obtain permanent residency on condition of honorable discharge.

Both ads feature Mexican-born, Chicago raised Alejandro Morales who was brought to the U.S. when he was a toddler and excelled in the Reserve Officers’ Training Corps (ROTC) member -- a college-based program that acts as a springboard to career military service.

"Don't let Congressman Steve King speak for you," says one of the ads in front of an image of the Marine Corps War Memorial in Rosslyn, Va.

Republican lawmakers, including Reps. Mo Brooks, R-Ala., and Louie Gohmert, R-Texas, oppose the ENLIST Act because they claim it rewards illegal immigration and lays the foundation of questionable loyalties in the armed forces. They also oppose the DREAM Act, which allows undocumented immigrants who came over as minors with no criminal records a fast track to permanent residency (and later citizenship) if they’re pursuing higher education.

FWD.us was founded by Zuckerberg and Joe Green, Zuckerberg’s Harvard colleague who went on to focus on online philanthropy and politically oriented social networking. The group supports comprehensive immigration reform that would allow undocumented immigrants who have exhibited a desire to stay in the country to contribute to the innovation economy. It also supports increasing the number of H-1B visas that would increase the number of foreign temporary workers used by tech and outsourcing companies.

Watch one of the ads here: