(NEXSTAR) — Shake Shack appears to be trolling Chick-fil-A with a new Sunday-only deal on sandwiches made with “antibiotic-free” chicken.

The NYC-based burger chain — which introduced chicken sandwiches to its menu over 8 years ago — took a few not-so-subtle jabs at Chick-fil-A when announcing the offer in a blog post last week.  

“Eat more antibiotic-free chicken,” the announcement began, in reference to Chick-fil-A’s longtime “Eat Mor Chickin” slogan.

“Here at Shake Shack, we pride ourselves on our Chicken Shack which is available 7 days a week,” the post continued, before mentioning that the sandwich is “made with antibiotic-free chicken, something not everyone can say these days…”

The post goes on to detail how customers can earn a free Chicken Shack sandwich with a minimum $10 purchase throughout the month of April. But the offer is only good on Sundays — a day which Chick-fil-A is famously closed.

Chick-fil-A had announced last month that its chicken sandwiches would no longer be made with antibiotic-free chicken due to supply issues. Instead, the chicken served at Chick-fil-A may contain “No Antibiotics Important To Human Medicine” (NAIHM), rather than no antibiotics at all.

“NAIHM restricts the use of those antibiotics that are important to human medicine and commonly used to treat people, and allows use of animal antibiotics only if the animal and those around it were to become sick,” the restaurant said in a statement.

A representative for Chick-fil-A was not immediately available to comment on Shake Shack’s deal.

Shake Shack, meanwhile, touted its Sunday-only offer in an X post shared Sunday (of course), with a graphic urging followers to “Eat More Chicken Shacks.”

One X user tagged Chick-fil-A in the comments section, hoping to get Chick-fil-A’s “thoughts” on Shake Shack’s provocative post.

“Might not hear back until tomorrow,” Shake Shack reminded the user.