Republican Sens. Jeff FlakeJeff FlakeObama FCC's 'privacy' rules were a sham Wounded Ryan faces new battle Overnight Tech: High court hears case on where patent suits are filed | House to vote on blocking internet privacy rules | Facebook's new tools for voters MORE (Ariz.), Saxby ChamblissSaxby ChamblissSpicer: Trump will 'help the team' if needed in Georgia special election Wyden hammers CIA chief over Senate spying Cruz is a liability MORE (Ga.), Johnny IsaksonJohnny IsaksonOvernight Finance: Senators spar over Wall Street at SEC pick's hearing | New CBO score for ObamaCare bill | Agency signs off on Trump DC hotel lease GOP senators offer bill to require spending cuts with debt-limit hikes Schumer to House GOP: 'Turn back before it's too late' MORE (Ga.), Dan CoatsDan CoatsMcCain says he hasn't met with Trump since inauguration Oversight committee asks White House, FBI for Flynn records Live coverage: FBI director testifies to Congress MORE (Ind.), Chuck GrassleyChuck GrassleyOvernight Finance: Dems seek probe of acting SEC chief | Defense hawks say they won't back short-term funding | Senate seen as start point for Trump infrastructure plan | Dems want more money for IRS Overnight Regulation: Trump administration lifts Obama freeze on federal coal mining Senators offer bill aimed at helping IRS whistleblowers MORE (Iowa), Susan CollinsSusan CollinsSenate braces for fallout over Supreme Court fight Overnight Finance: WH wants to slash billions | Border wall funding likely on hold | Wells Fargo to pay 0M over unauthorized accounts | Dems debate revamping consumer board Lawmakers call for pilot program to test for energy sector vulnerabilities MORE (Maine), Dean HellerDean HellerWith GOP’s healthcare bill on ice, Dems go on offense Red-state Dems in Supreme Court pressure cooker This week: House GOP faces make-or-break moment on ObamaCare MORE (Nev.), Kelly AyotteKelly AyotteFEC commissioner to Trump: Prove voter fraud Live coverage: Day three of Supreme Court nominee hearing Lewandowski saw no evidence of voter fraud in New Hampshire MORE (N.H.), Rob PortmanRob PortmanMcCaskill investigating opioid producers Overnight Finance: Senators spar over Wall Street at SEC pick's hearing | New CBO score for ObamaCare bill | Agency signs off on Trump DC hotel lease GOP senators offer bill to require spending cuts with debt-limit hikes MORE (Ohio) and Ted CruzTed CruzTexas Dem targets Sen. Ted Cruz in 2018 What are 'religious liberty' bills really about? Fiorina calls for special prosecutor for Russia probe MORE (Texas), as well as Democratic Sen. Martin HeinrichMartin HeinrichLawmakers call for pilot program to test for energy sector vulnerabilities The Hill’s Whip List: 32 Dems are against Trump’s Supreme Court nominee Senators demand Pentagon action after nude photo scandal MORE (N.M.), are being targeted in the effort.

The ads, which will run on Facebook and on search engines, ask supporters to call the individual senators and express support for expanded gun-control measures.

"Too many Americans are dying from gun violence & Congress needs to act. Call Sen. Collins!" reads the ad running against Collins.

The Senate will begin consideration of a comprehensive gun control bill this week or next; it's still unclear whether President Obama will be able to successfully rally support for one of the most politically feasible measures — universal background checks for gun owners.

Opposition from Republicans and some red-state Democrats has resulted in other Obama priorities, including an assault-weapons ban, being stripped from the main bill.

The passage of universal background checks is largely considered the test of whether Obama's push for expanded gun control measures, which followed the Sandy Hook massacre late last year, has been a success.

The president spent Monday in Hartford, Conn., speaking in support of his effort to reduce gun violence. Vice President Biden and Attorney General Eric HolderEric H. HolderUber donates M to supporting minorities in tech Overnight Tech: Senate moving to kill FCC's internet privacy rules | Bill Gates pushes for foreign aid | Verizon, AT&T pull Google ads | Q&A with IBM's VP for cyber threat intel Uber leadership sticking by CEO MORE will address the issue on Tuesday at the White House, and first lady Michelle ObamaMichelle ObamaReport: Bush called Trump's inauguration speech 'some weird s--t' Obama to travel to South Pacific island to work on memoir: report Obama and Trump haven’t talked since inauguration MORE will advocate for the package at a speech in Chicago later in the week.

The OFA has been working to support his lobbying effort, issuing ads against 16 GOP lawmakers earlier this year. It hopes the online ad campaigns will pressure some of the 11 senators to support the final bill.

While many of the senators targeted in the new ad push reside in red states where any expansion of gun control measures is unlikely to be politically palatable, some — like Collins and Ayotte — are in states that lean blue and might be open to the bill.

Collins is up for reelection in 2014, and a vote for the gun control bill could give her a boost among Democrats and centrists in Maine.

Chambliss, too, represents a possible GOP vote in favor of a bill, as he's retiring in 2014.

Top aides to the president’s reelection effort relaunched his campaign arm, Obama for America, as the new OFA in January. Now a nonprofit, Organizing for Action can, by law, engage in issue advocacy but not electoral politics. 

It can also receive unlimited donations, and does not have to disclose its donors.

The group has come under fire by campaign finance reform advocates who have expressed concern that special interests can buy “access” to the president through contributions to his advocacy arm, but the group has said it will voluntarily disclose donors.

--This post was updated at 11:33 a.m. on Tuesday.