Dubai carrier Emirates, also a major sponsor, declined to comment on the bribery allegations
Drinks giant Coca-Cola has become the latest World Cup sponsor to call on soccer's rulers to deal thoroughly with allegations of bribery to secure the 2022 World Cup for Qatar, an issue overshadowing this week's kickoff in Brazil. Adidas, Sony and Visa earlier this week also expressed their concerns.
With its four yearly showpiece event only four days away, soccer's governing body FIFA is on the defensive, conducting an internal investigation into the decisions to hold the 2018 World Cup in Russia and the 2022 Cup in Qatar. Both countries have denied any wrongdoing.
Qatar's bid has attracted controversy from the outset because of the extreme summer heat during the months when the Cup is played and the tiny country's lack of domestic soccer tradition. If it goes ahead, the tournament is expected to be switched to a date later in the year, creating scheduling headaches for broadcasters and European club soccer clubs.
The signs of unease from some of FIFA's paymasters will raise pressure on the body, led by its 78-year-old Swiss president Sepp Blatter, to get to the bottom of the allegations and tackle underlying concerns about how it is run.
"The negative tenor of the public debate around FIFA at the moment is neither good for football nor for FIFA and its partners," said German sportswear company Adidas, which has signed up as FIFA sponsor until 2030, extending a partnership dating back to 1970.
"Anything that detracts from the mission and ideals of the FIFA World Cup is a concern to us," a company statement read.
"But we are confident that FIFA is taking these allegations very seriously and is investigating them thoroughly through the Investigatory Chamber of the FIFA Ethics Committee.
"The FIFA World Cup is a platform that unites people all over the world, inspiring and celebrating the world's most popular sport while creating memorable experiences for athletes and fans. We believe that through our partnership and continued involvement with FIFA we can help foster optimism and unity, while making a positive difference in the communities we serve."
Britain's Sunday Times newspaper has over the last two weekends printed what it says are leaked documents showing bribes were paid to secure the event for Qatar, which Qatar denies.
Former U.S. prosecutor Michael Garcia, leading FIFA's internal investigation, is due to report in July, around a week after this year's World Cup final.
FIFA issued a statement from the body's marketing director Thierry Weil as it sought to take heat out of the situation.
"We are in constant contact with our Commercial Affiliates including Adidas, Sony and Visa and they have 100 percent confidence in the investigation currently being conducted by FIFA's independent Ethics Committee," Weil said.
"Our sponsors have not requested anything that is not covered by the on-going investigation by the Ethics Committee."
Payment card company Visa, which has a contract as a FIFA sponsor until 2022, said it was monitoring the progress of the Garcia investigation.
"We expect FIFA will take the appropriate actions to respond to the report and its recommendations," it said in a statement.
Japanese consumer goods company Sony took a similar line, saying said it expected the allegations to be "investigated appropriately".
It is unusual for sponsors to say anything publicly on such a sensitive issue and the comments reflect concern over the knock-on effects on their image.
"This underlines that companies need to make sure that any high profile association enhances their reputation rather than damages it," said Andy Sutherden, Global Head of Sports Marketing & Sponsorship at communications firm H+K Strategies.
FIFA, which Blatter has led since 1998, earned almost $1.4 billion last year, including more than $600 million from the sale of broadcasting rights and more than $400 million from sponsors and other marketing partners.
Sony, Adidas, Visa and Coca-Cola are among six main FIFA sponsors who collectively paid around $180 million last year. Sony's sponsorship agreement, which also included the 2010 World Cup, expires this year, giving it particular leverage as it negotiates a new deal.
Airline Emirates, whose sponsorship deal is also up for renewal at the end of the year, declined to comment.
South Korean carmaker Kia Motors Corp, which shares sponsorship of the tournament with its affiliate Hyundai Motor Co, said in a statement: "We are confident that FIFA is taking these allegations seriously and that the Investigatory Chamber of the FIFA Ethics Committee will conduct a thorough investigation."
The Sunday Times printed new accusations on Sunday, just four days before the 2014 tournament kicks off in Brazil, alleging that then-Asian football chief Mohamed Bin Hammam, a Qatari, had brokered meetings between Qatari officials and governments to discuss bilateral trade deals.
Qatar denies Bin Hammam was connected to its bid for the Cup. Bin Hammam has not commented. FIFA has already banned Bin Hammam for life from soccer over accusations he paid bribes to win votes for a bid to become FIFA president. That ban was overturned but another was imposed for conflicts of interest.
FIFA is now facing calls to strip Qatar of the World Cup should Garcia's investigation prove that it bought the votes needed to host the tournament.
The United States, Australia, Japan and South Korea were the rivals who lost out to Qatar in the 2010 vote and are all safer choices as former hosts of major sporting events and developed markets for consumer brands.
US broadcaster Fox, which paid an estimated $425m for rights to the 2018 and 2022 World Cups, was already unhappy with plans to switch the dates of the Qatar tournament to later in the calendar year when it would clash with the NFL American football programme.
Both fans and sponsors would be likely to cheer a switch to a different venue, although Qatar would be certain to mount a legal challenge to keep the Cup.
"None of the sponsors would want it to be held in Qatar," said David Peters, managing director of marketing company Dentsu Aegis Network Sport & Entertainment.
"FIFA haven't given a great deal of consideration to sponsors. The sport is so big, they are less beholden than other sports," he added.