Alkass Digital
Ten horse racing trainers have received phone calls from someone claiming to be the "acid man", who threatened to spray acid in their faces.
Those targeted include six-time champion jumps trainer Nicky Henderson, Gary Moore and flat trainers Charlie Fellowes and Richard Fahey.
The National Trainers Federation (NTF) reported the threats from earlier this month to police, who are investigating.
"It's pretty horrendous stuff," said NTF chief executive Paul Johnson.
Essex Police said it was investigating "a number of reports of malicious communications" on 10 November which it believes were linked.
Speaking to BBC Sport, Johnson said: "The specific threat itself was from somebody claiming to be 'the acid man' and - there are slightly different versions of the same story - that they would tap the trainer on the shoulder at the racecourse next time they saw them and they would spray acid in their face."
Johnson said trainers were used to receiving abuse but this was a reminder that "it is not acceptable", while individual jockeys have also been targeted in the past.
Saffie Osborne was sent death threats in 2021 which led Lucy Snowden, wife of trainer Jamie Snowden, to set up an initiative where people in the sport could report abuse.
The initiative was widened by the NTF and this was where the trainers reported the acid threats.
In a statement, Essex Police said: "We're investigating a number of reports of malicious communications which took place on November 10 2023.
"We are continuing to assess the reports and, at this stage, we are linking each of them. In total, 10 victims have been identified and our investigation is ongoing."