The organisers of the International Eisteddfod in Llangollen have called on the UK Government to be more flexible with performers' visas.
Organisers have said that more overseas competitors than usual have had to pull out or will arrive late.
This year, an Indian dance group has only been able to bring 19 of its 38 members and a Ukrainian folk group will not arrive in time due to visa delays.
The Home Office said all cases were decided by strict immigration rules.
The festival, which started in the north Wales town on Tuesday, attracts hundreds of entertainers from all over the world.
Visa problems have been experienced at past festivals, but organisers said that problems has worsened ahead of this year's event.
Eisteddfod organisers claim the government may be clamping down after allegations of lax entry procedure to the UK from Romania and Bulgaria earlier this year.
They have called for the authorities to be more understanding towards their event.
Last week, a group of Ukrainian singers, Versalko, which was due to perform at Llangollen staged a sit-in protest at Kiev's British Embassy.
The 28 performers had refused to leave until they received the necessary documents to come to Wales.
Versalko have preformed at Llangollen before
They finally received their visas on Monday, but will not arrive at Llangollen until Wednesday - in time to perform, but too late to take part in a competition they had entered.
Keith Hall, The Eisteddfod's competitors liaison officer, said: "I know that Bulgaria and Romania earlier on in the year had visa problems, and whether it's a knee jerk reaction to that, I can't really say.
"Obviously the embassy officials have instructions, and they seem to be applying those instructions quite rigidly.
"Although I can understand the reasons for so doing, at the same time they have to take heed of what these groups are coming for.
"I'm sure a lot of the officials in the embassies have no idea what the groups are coming to.
"It is the worst certainly that I can remember in more than 10 years of doing this job.
"We were due to have 2,300 overseas competitors taking part, but the number has fallen to 1700 - mainly because people can't get visas".
The Home Office said that immigration rules were simply being followed.
A Home Office spokesperson said: "We cannot comment on individual immigration cases.
"Anyone entering the UK must satisfy immigration officers they meet the immigration rules.
"An entertainer needing a visa to visit the UK would obtain this from a British diplomatic mission abroad.
"Applications are decided in accordance with the immigration rules.
"Entertainers seeking to take part in an event in the UK would need to produce appropriate documentation, including evidence that they were to take part in a particular event.
"On arrival in the UK the authenticity of the visa would be verified and visa holders are allowed to proceed once entry checks are complete."