Donald Trump’s veiled threat against nations that may oppose the US bid to co-host the 2026 World Cup has prompted Fifa to refer to guidelines that warn against political influence over bids. Morocco is the the only other rival to the US, which has launched a joint bid with Canada and Mexico.

“The U.S. has put together a STRONG bid w/ Canada & Mexico for the 2026 World Cup,” Trump tweeted. “It would be a shame if countries that we always support were to lobby against the U.S. bid. Why should we be supporting these countries when they don’t support us (including at the United Nations)?”

The U.S. has put together a STRONG bid w/ Canada & Mexico for the 2026 World Cup. It would be a shame if countries that we always support were to lobby against the U.S. bid. Why should we be supporting these countries when they don’t support us (including at the United Nations)? — Donald J. Trump (@realDonaldTrump) April 26, 2018

Fifa will choose the hosts at a meeting in Moscow on 13 June. “As a general rule, we cannot comment on specific statements in connection with the bidding process,” said Fifa in a statement. “We can only refer to the Fifa regulations for the selection of the venue for the final competition of the 2026 Fifa World Cup, and in particular to the bid rules of conduct incorporated therein.”

The bid rules contain an explicit warning against activities by bidding country governments which “may adversely affect the integrity of the Bidding Process and create an undue influence on the Bidding Process.”

Mexico’s president, Enrique Pena Nieto, responded positively to Trump’s tweet. “We can have differences but football unites us. Together we support the candidacy of Mexico, Canada and USA as the headquarters of the World Cup 2026,” he wrote on Twitter.

The North American bid committee said it was pleased to have Trump’s support. “From the beginning, we have received strong support from the Canadian, Mexican, and United States governments. We are grateful for that support and together our three countries are ready to welcome players and fans from around the world to an extraordinary Fifa World Cup in 2026.”

The Moroccan bid team declined to comment on Trump’s tweet.

The North American bid boasts large stadiums and excellent infrastructure but is no certainty to win the June vote. The Morocco bid is expected to receive strong backing from Fifa’s African and Middle East members.

France plans to back Morocco, the country’s football federation president told local media recently, while Russia, which will host the 2018 tournament this summer has said it will also vote for the north African nation’s bid.

The United States previously hosted the World Cup in 1994. Fifa member countries receive one vote each, no matter their size.