A witness said The Marsh Hotel pub on Bradford Road in Cleckheaton was hosting its popular weekly poker night when three men dressed in balaclavas and wielding weapons burst through the doors and told the eight men present to "get down on the floor or we'll spray you with acid".
The witness described how one of the gang collected their wallets while another told a member of staff - believed to be the pub's landlord - to show them to the safe.
When he refused the suspect threw a substance over him which caused him to fall to the floor and suffer breathing difficulties. The nature of the substance is yet to have been confirmed by emergency services.
He then got back to his feet but was then attacked with an axe, causing him to fall to the floor again.
When on the floor he was again sprayed with the unknown substance. He suffered injuries to his lip and irritation to the skin.
A second man who had just left the pub was also sprayed in the face with an unknown substance and forced back inside. He was not injured during the incident.
"It was awful," said one of the men threatened, a 48-year-old man from Cleckheaton, "this is what society has become.
"I'm shaken - it's not a feeling that's going to leave me in a hurry. I feel sorry for the guys that were injured."
A witness said the trio made off with thousands of pounds in cash.
One of the males officers want to speak to in connection with the incident is described as white and wearing a black top with the hood up covering most of his face.
A second male is described as white and wearing a light coloured hooded top with black clothing covering some of his face. It is thought this male had been in the area of the pub prior to the incident.
A third male is described as wearing a balaclava and one of the three is also believed to have had a hammer on them.
Detective Inspector Alex Bacon of Kirklees CID, said: “This was a serious incident which has traumatized the victims.
“Two people have been sprayed with a substance which has caused them great distress and one person attacked with what is believed to be an axe.
“Thankfully at this stage we don’t believe anyone was seriously injured but the pub was still open at the time and with it being a bank holiday weekend there will have been a lot of people around the area.
“I want to appeal directly to anyone who saw anything suspicious either immediately before or after the incident to get in touch.”
Anyone with any information is asked to call police on 101 quoting crime reference 13190231642 or the independent crime fighting charity Crimestoppers, on 0800 555111.