The brawl between the two travel heavyweights started with a July 29th article in Spain's El Mundo newspaper.
The piece recounted how the son of one of the victims — the paper gave his only name as Ángel — had tried to book Ryanair flights from Madrid to the northern city of Santiago de Compostela using the flight search engine Rumbo on the morning after the June 24th train accident.
At 6am he booked two flights for a total of €471 ($627). He was then told to wait for an email confirming for the reservation.
Two hours then passed without the email arriving.
El Mundo then reported that when Ángel's partner Elisa called Rumbo, the company said they had been unable to confirm the booking because Ryanair had bumped prices up to a total of €800 for the two passengers.
The couple then decided to drive 600km (373 miles) to Santiago de Compostela because they didn't "want don't anyone to make money" out of their "misfortune".
But now Ryanair and Rumbo are engaged in a public relations battle with both sides asserting they didn't raise the prices of the tickets.
On August 8th, lawyers acting for Ryanair contacted Rumbo asking for the matter to be cleared up.
In a fax sent to the Madrid-based company, lawyers for the Irish airline said internal investigations had revealed no record of bookings for two customers called Ángel and Elisa.
Ryanair also said it could demonstrate that none of the three Madrid—Santiago flights on July 25th had individual seat prices of €400.
In their fax, the carrier asked Rumbo to confirm that they had never made bookings for Ángel and Elisa.
They also asked the Spanish firm to state that the couple's flight reservation had not been cancelled because Ryanair had increased prices.
The airline asked for this confirmation to be provided by August 12th or legal action would be taken. That date has now passed.
Travel search engine Rumbo, meanwhile, issued a statement in which they said they have no influence over airline prices.
"Rumbo, as a travel agency, acts as an intermediary between airline companies and the client , providing comparison and booking services," said the company.
"Availability and flight prices are published by the airline carriers," Rumbo added in its statement.
On Monday, Spain's Confederation of Housewives' Organizations, Consumers and Users (CEACCU) entered the fray, but going after both parties rather than taking sides.
Acting on behalf of families of victims of the train crash, the CEACCU has taken the issue to authorities in Galicia, where the accident happened.
They are claiming the sudden increase in ticket prices forced some families to take alternative transport in the wake of the crash.
The rise in prices was "unfair and liable to administrative sanctions", the association said.
The CEACCU wants believes Rumbo and Ryanair could be liable for fines ranging from €15,000 to €16,000.