The French state railway company SNCF has called for police action against cyclists in the Paris-Roubaix spring classic who crossed tracks with a safety barrier down, seconds before a high-speed train arrived.
The incident happened at a crossing in northern France during Sunday's race.
The SNCF has issued a statement calling for "several riders" to be prosecuted for acting "against all safety rules".
Race organisers have said the riders could not stop in time.
"Millions of television viewers saw live this extremely serious and irresponsible action which could have been tragic," said SNCF.
"A few seconds later, a TGV ran on this line and could have hit the peloton."
The barriers went down while the peleton was approaching at about 37mph.
SNCF spokesman Christophe Piednoel said the train and the riders, who were 10 minutes ahead of schedule because of a strong tail wind, were not supposed to arrive at the crossing at the same time.
Some riders managed to go through, but a police motorcycle stopped others in the 151-mile race.
French champion Arnaud Demare said: "This needs to be taken care of. It was dangerous. We went through but it was close."
Race organisers said on Sunday they would not punish the riders.
"It wasn't possible for the leading riders to stop sufficiently safely," said Guy Dobbelaere, president of the jury of race commissioners. "The peloton was 10 metres away when the barrier started to close."
Sunday's race featured 10 level crossings and was also disrupted last year by barriers coming down as an eight-man breakaway group approached.
The International Cycling Union (UCI) described the incident as "extremely worrying" and has requested a comprehensive report from race organisers.
Sir Bradley Wiggins finished 18th in what was his final race for Team Sky, 31 seconds behind German winner John Degenkolb.