London (CNN) -- U2 frontman Bono is usually lauded as one of the world's most vocal anti-poverty campaigners but at Glastonbury Festival on Friday he instead found himself the target of criticism at his band's alleged efforts to avoid paying millions of euros in taxes.

Protesters had planned to unveil a "visual spectacle" during the headlining performance by the group -- whose wealth was estimated by the Sunday Times last month at 506 million euros ($720 million) -- at the festival in western England.

As U2 took to the stage, activists from Art Uncut inflated a 20-foot balloon bearing the words "U Pay Your Tax 2," according to the UK's Press Association. But security guards reportedly wrestled them to the ground before deflating the balloon and removing it.

U2 was criticized in 2006 when the band, fronted by singer Bono and whose hits include "I Still Haven't Found What I'm Looking For," reportedly shifted much of its business affairs from Ireland to the Netherlands. That move came after the Irish government reduced tax breaks for income earned from "works of artistic merit."

Art Uncut said Bono was hypocritical in campaigning about poverty while seeking to reduce the amount he paid in taxes. "Bono is well known for his anti-poverty campaigning but tax avoidance by multi-national companies and rich individuals is a massive problem for the developing world," the group's spokesman Steve Taylor told CNN.

"The developing world, which Bono professes to care so much about, loses more through tax avoidance each year than it receives in aid. By moving their business abroad, Bono is very much a part of that problem. There is an element of hypocrisy here."

"U2 are avoiding paying millions of euros in tax. This comes at a time when the people of Ireland are experiencing extremely harsh cuts in their public services, among the harshest in Europe. The money that's nestling in U2's bank account really should be helping to offset some of the pain that the Irish are experiencing at the moment.

"We realize that Bono has done some good stuff on poverty but I don't think he realizes how much of a problem tax avoidance is for the people of Ireland and for those in the developing world."

U2's management company declined to comment on the criticism. However, the charity ONE, co-founded by Bono to fight poverty and preventable diseases in the developing world, said the protest was misguided.

"We're all for noise in the fight against extreme poverty, but this protest is barking up the wrong tree," Jamie Drummond, cofounder and executive director of ONE, said. "I've been campaigning on development issues for many years and seen a fair amount of Bono-bashing. It's an easy way for people to get publicity."

"Campaigns supported by Glastonbury and musicians like Bono and Youssou N'Dour in the past have achieved incredible results. Take Drop the Debt and Make Poverty History -- supported by U2 along with most of the music world and Glastonbury-goers alike. These campaigns have helped get over 46 million more African kids into school and averted millions of child deaths through vaccinations against preventable diseases.

"In the fight against extreme poverty, the real issue activists should be concerned about is the lack of transparency in some offshore financial centers which help corrupt officials and corporations working in developing countries to steal money out of those developing country economies. This has nothing whatsoever to do with U2's business affairs."

But one Irish academic said it was incompatible for Bono to be preaching about reducing poverty on the one hand while promoting tax avoidance with the other.

"People can send aid to the global south but if the global south can mobilize domestic revenue that would be a whole lot more sustainable," said Sheila Killian, head of accounting and finance department at the University of Limerick. "So the whole issue of tax and development is one that he might not fully understand."

Bono had lost a great deal of respect in Ireland in 2006 when he moved his affairs, she added. "Bono doesn't earn billions, and not enough to rescue Ireland's calamitous economic situation, but there's an inconsistency in his attitude."

If Bono were to pay his full share of revenue in Ireland, "he could help send out a very strong signal for people to pay their fair share of tax."