(CNN) - Republican Sen. Jeff Flake of Arizona had two words to conservatives who want him to back a government shutdown threat in their effort to defund Obamacare:
He posted that short message to Twitter on Monday evening along with a link to a radio ad from the Senate Conservatives Fund that claimed he wouldn't "stand up to President Obama and join conservatives in pledging to oppose funding for the implementation of Obamacare."
Republicans are divided over how to handle the health care law as they approach one of two fiscal deadlines. Funding for the federal government is set to expire at the end of September, and separately, the Treasury Department will run out of the "extraordinary measures" it has employed to avoid default since hitting the debt ceiling in May. Treasury said Monday it expects to reach the limit of those measures in mid-October.
But it is the September 30 deadline on which Republicans are focused. Some say they would support a continuing resolution to keep the government open on the condition it blocks funding for the president's signature health reform legislation.
Others, including Flake, stress their opposition to Obamacare but say it's unrealistic to expect Democrats, including Obama, to sign on to such a measure.
Speaking at a luncheon last week, he said of a government shutdown to block the law: "I agree with the goal, but not the tactic," according to the Arizona Daily Sun.
Arizona's other Republican senator, John McCain, has also said he does not support the shutdown threat.
Costing $31,750, the radio ad begins a two-week statewide run on Tuesday, the Senate Conservatives Fund said.