The folks at Catholics United, a progressive Catholic group, have been busy NOT putting fliers in church parking lots. They view that as an intrusion. Indeed, what they’ve been doing instead is making sure that flyers that do get put there are removed.
A report from the group’s director Chris Korzen:

“We had staff and activitsts in 6 cities: Philly, Pgh, STL, Cincy, Detroit, and
Akron-Youngstown. By far the most effective strategy was simply to let
church officials (ushers, etc.) know what was going on. Once informed,
these officials usually went outside and asked the leafleters to leave.
The leafleters I encountered were not parishioners of the churches they were
targeting, and for the most part were belligerent and rude. At one parish
in Montgomery County, a church official had to threaten to call the police
in order to get the Priests for Life activists to leave.
Another parish in the Philly burbs was hit by the PA Republican Party on
Saturday night. When one of our activsts went by on Sunday morning she
found a very stern looking woman watching over the parking lot – and no more
literature.
And finally, I’m sitting on about 100 reports of parish protection
operations from our activists in all corners of the country. All in all,
incredbily successful.”

What, you might ask, is a “parish protection operation”? Korzen explains:

“Simply put, we’ve organized our activists to protect the sacred space of the
church from partisan politics, in accordance with the USCCB’s directive that
only approved voter education materials be distributed on Church property
and at Church events. It’s noteworthy that we’ve consistently asked our own
activists to distribute Catholics United literature on Church property only
with the permission of their pastor. The religious right, apparently, does
not respect the Bishops’ directive.”