Planned Parenthood mailers defaced with threatening messages were found last week in the mailboxes of several residents in Apple Valley, Minnesota. The mailers were defaced with the words “death” and “die,” and reproductive rights advocates view the incident as part of an escalating attack on abortion providers.

The U.S. Postal Service is reportedly investigating the incident.

Nika Davies, a resident of Apple Valley, told KMSP that she found the mailers “disconcerting” because she could not identify who had sent the mailers. “I didn’t feel threatened until later and then thought, ‘I don’t like getting anything that says “death” on it,'” Davies said.

Planned Parenthood operates 17 reproductive health care facilities throughout Minnesota, including Apple Valley, a suburb of the greater Minneapolis-Saint Paul metropolitan area. The Planned Parenthood Apple Valley clinic does not provide abortion services.

These threats come as abortion providers across the United States face increased levels of harassment and threats of violence, which has affected the ability of pregnant people to access abortion care.

duVergne Gaines, director of the Feminist Majority Foundation’s National Clinic Access Project, told Rewire that abortion providers have long been a target of intimidation and harassment, but the apparent targeting of Planned Parenthood supporters is especially troubling.

“This kind of act, which is intended not only to intimidate abortion providers and Planned Parenthood … is also intended to intimidate people who support Planned Parenthood. I think that is something I find very insidious about this particular act,” Gaines said.

Gaines believes that the increasingly hostile rhetoric from lawmakers opposed to abortion rights and misinformation campaigns that have been propagated by conservative media have contributed to a hostile climate for abortion care providers.

“I think that the rhetoric by some of these lawmakers is irresponsible and reckless,” Gaines said. “It places physicians and women’s health care providers in the scope of these extremists, and helps declare an open season on them.”

State Rep. Erin Maye Quade (D-Apple Valley), told KMSP that her parents received one of the defaced mailers, and it seems like a “targeted attack” on the people who received the mailers. “We know there is heavy rhetoric surrounding the issue of pro-choice, anti-choice, so having ‘die’ on your mail is not only a crime, but it is very scary,” Quade said.

Gov. Mark Dayton (D) in May vetoed a pair of anti-choice bills passed by the Republican-controlled state legislature.

This year abortion clinics have been subjected to large scale protests and threats of violence. Radical anti-choice activists descended on Louisville in May and laid siege to Kentucky’s last remaining abortion clinic, and an abortion clinic in Virginia received a bomb threat in April.

Abortion clinics throughout the country face an unrelenting and increasing amount of anti-choice harassment and threats, according to a report by the National Abortion Federation (NAF).

In 2016, clinics across the country reported nearly 43,000 incidents of hate mail and internet harassment, compared to nearly 26,000 incidents in 2015. Clinics reported nearly 62,000 instances of picketing during 2016, compared to around 22,000 instances in 2015.

“There are providers in every state of the union that are experiencing this rise in extremely virulent protests whose conduct is crossing the line from free speech into possibly stalking, trespassing, threatening,” Gaines said. “That is happening now on such a large and wide scale that it is incredibly concerning.”

Planned Parenthood of Minnesota, North Dakota, South Dakota told Rewire that the organization could not comment on the incident due to the ongoing investigation.

The USPS confirmed that there is an investigation into the incident, and said in a statement to KMSP that it is unknown whether the threats were from a postal service employee or another person.