Duncan Scott refused to acknowledge gold medallist Sun Yang after claiming a share of bronze in the men's 200m freestyle at the World Aquatics Championship in Gwangju.
The sport's governing body, FINA, issued both Scott and Yang with warning letters as a result of their conduct during the ceremonies.
Chinese swimmer Sun – who has previously served a doping ban – won the title only after his rival Danas Rapsys, who touched home first in one minute 45.78 seconds, was belatedly disqualified for a false start.
Scott, who dead-heated with Russia's Martin Malyutin behind silver medallist Katsuhiro Matsumoto of Japan – observed the national anthem but then refused to join the traditional podium photo.
In response, Sun turned towards Scott as the medallists left the stage and appeared to tell him: "You're a loser – I'm a winner."
FINA later announced the pair faced the same sanction meted out to Australian swimmer Mack Horton, who refused to share the podium with Sun after taking silver behind the Chinese swimmer in the men's 400m freestyle event.
Britain's Duncan Scott making the latest stand for clean sport, echoing Mack Horton's refusal to shake hands or pose for photos on the podium with Sun Yang. Some strong words of frustration from Sun afterwards – no bite from Duncan, just quiet defiance.#Gwangju19 #CleanSport pic.twitter.com/Qb50Q2Af30 — Lizzie Simmonds (@LizzieSimmonds1) July 23, 2019
Referring to Horton's original stance, Scott told the BBC: "I'm team Mack. If [Sun] can't respect our sport, then why should I respect him? Hopefully this will happen in more events."
Scott's stance appeared to be cheered by a majority in the stadium, barring a vocal group of Chinese supporters who celebrated Sun's victory.
Aside from his previous drugs ban, Sun currently faces a hearing at the Court of Arbitration for Sport over a decision to clear him of a further doping offence, and many of his rivals believe he should not be competing.
The bronze was the fourth World Championships medal of Scott's career and his first in an individual event, having earned gold as part of the 4x200m freestyle relay squad in both 2015 and 2017 and 4x100m medley silver on the latter occasion.
After a meeting of its executive board, FINA found both swimmers "guilty of inadequate behaviour on this occasion, which is not acceptable in accordance with the FINA Constitution Rule C 12.1.3".
British Swimming was not immediately available to comment on Scott's sanction.
However, Great Britain's former world medallist Lizzie Simmonds wrote on Twitter: "What Mack and Duncan have done, in the face of jeers, taunts and aggression, has shown impressive strength of character.
"It takes a huge amount of courage to stand against the status quo and lead the way to change."
Adam Peaty cruised into the final of the men's 50m breaststroke.
One day after picking up his third consecutive 100m crown, Peaty beat his nearest rivals by over half a second as he finished in 26.11 seconds.
Peaty will hope to go close to his own 50m world record of 25.95secs – which he set in 2017 in Budapest – in the final on Wednesday.
