Sen. Jeff Flake (R-Ariz.) is among the targets of an effort to pressure conservative lawmakers into supporting a proposal to defund the Affordable Care Act.

In the latest ad campaign by the Senate Conservatives Fund, Flake is one of seven senators individually accused of "not standing up to President Obama."

"This could be our last chance to stop Obamacare," said the ad. "It's time for Jeff Flake to get off the sideline and join the fight today."

To this, Flake offered two words in a tweet:

Flake will appear with Sen. John McCain (R-Ariz.) at an immigration forum in Arizona Tuesday. The same day, a six-state, five-day tour to similarly pressure GOP lawmakers like Flake will begin in Kentucky.

Given the shrinking time before the Affordable Care Act takes effect, both Flake and McCain might receive questions on their lack of support for the "defund Obamacare" movement. Flake has not taken a position on the issue. McCain has stated he will not support the defunding proposal.