Chinese authorities have hardened their line on foreign musicians, after Elton John infuriated them by dedicating a performance to outspoken artist and activist Ai Weiwei, according to industry sources. Police arrived to interview the singer shortly after he announced that the performance, which took place in Beijing last November, was dedicated "to the spirit and talent of Ai Weiwei", according to two sources. One said officers wanted John's manager to sign a statement saying the dedication was inspired only by admiration for Ai's art. John's spokesman declined to comment when contacted by the Guardian.

Ai and John met briefly before the Beijing show, with Ai subsequently announcing to fans on Twitter: "I super like him." John was allowed to go ahead with a scheduled concert in Guangzhou in early December. But the English language edition of state-run newspaper Global Times attacked John. It said the singer was "disrespectful" when he "forcibly added political content to the concert", adding: "If they had known that this concert would be dedicated to Ai Weiwei, many in the audience would not have come.

"John's action will also make the relevant agencies further hesitate in future when they invite foreign artists ... [He] has raised difficulties for future arts exchanges between China and other countries," the newspaper said in an editorial.

The singer's remarks even prompted the culture minister, Cai Wu, to demand that only stars with university degrees be allowed to play in China in future, according to two sources. They said that days after the concert, Cai gathered those who deal with visiting foreign artists and announced that only graduates should be given performance licences. One source said officials believed it would be difficult to implement the edict, and both suggested it may have been a spur of the moment comment.

A culture ministry spokesman said there were no new regulations. They did not address specific questions that the Guardian had asked regarding the meeting, replying: "About what you said in the fax, there is no such thing".

Another source said that since the start of the year, classical musicians had been required to supply proof of degrees and other qualifications when applying for permission to tour China. "There is no doubt at all it has made things harder," said one of those with knowledge of the meeting, adding that several recent applications for licences had been rejected.

"They are looking closely at videos, making sure that the people on stage are exactly the same as in the visa applications, and so on. It's not a change in the rules as much as a tightening [of existing procedures]."

A fourth source said he was not aware of the ministerial meeting, but that local cultural officials had summoned promoters within a fortnight of the incident to remind them of event rules, which included appearances by foreign artists.

Scrutiny of visiting musicians was tightened in 2008 after Björk shouted "Tibet! Tibet!" at the end of her song Declare Independence during a performance in Shanghai. China's ministry of culture later said that "[her] political show has not only broken Chinese laws and regulations, and hurt the feeling of Chinese people, but also went against the professional code of an artist".

A ban on artists who did not make it to university would have kept out both John and Björk, neither of whom have degrees.

The ministry of culture monitors music for vulgarity, as well as political content. In 2009, it ordered a cleanup of online music sites to address "poor taste and vulgar content".