Some antiabortion groups have held back from calling for a government shutdown because of uncertainty over what it would accomplish.

“Our position is that the House must send a [short-term spending bill] that defunds Planned Parenthood to the Senate,” said Mallory Quigley, a spokeswoman for Susan B. Anthony List, which supports antiabortion candidates. “There are differences between the pro-life groups on that, but our opinion is that the fight is important morally and politically.”

Americans United for Life, an antiabortion group, hasn’t taken a position on a possible shutdown, although they do believe Planned Parenthood should be defunded.

Pressure to defund Planned Parenthood will mount as a House Energy and Commerce subcommittee holds a hearing Thursday on two bills that would strip federal funding from providers who violate federal abortion laws.