Lukashenko says monitors are plotting against him
Tension is growing in Belarus ahead of presidential elections due on 9 September.
Belarus' electoral authorities have issued a formal warning to the leading opposition candidate, Vladimir Goncharik, over his use of campaign materials they found unacceptable, such as unregistered brochures and election posters.
The shirts are emblazoned with the slogan "Say No to the Idiot!" - the call-sign of a youth group opposed to President Alexander Lukashenko.
The election campaign in Belarus has become bad-tempered in recent days.
There has been little debate about manifestos or policies.
Instead, President Lukashenko and his opponents have been trading increasingly extravagant accusations.
European 'plot'
President Lukashenko said that the head of a European monitoring group in Belarus was deliberately provoking the country's authorities into his expulsion from Belarus, in order to discredit his campaign for a second, seven-year term in office.
He added that the authorities would remove the monitors as soon as the election was over, to avoid what he called a "Yugoslavia scenario" developing in Belarus.
About 300 international monitors are due to arrive in the country to observe the last days of the election campaign and the voting itself.
The country's authorities have already suggested the monitors' real purpose is actually to spy on Belarus - a claim rejected by the OSCE.
For its part, the European organisation has already pointed out that Mr Lukashenko's opponents in the election race are being discriminated against in the official media and that some election procedures fall well short of European standards.
Absolute power
Mr Lukashenko has concentrated power in Belarus and has displayed little tolerance for dissent.
His country is home to an authoritarian regime often compared to that of deposed Yugoslav President Slobodan Milosevic.
Non-governmental organisations and the independent media have often been targeted by the Belarus leadership.
But there is a general acceptance amongst ordinary Belarussians of the omnipotence of the country's authorities and draconian measures to preserve what Mr Lukashenko calls "order".
Death squad
Belarus has paid a heavy price for Mr Lukashenko's policies.
The Belarussian public has been rocked in recent weeks by revelations connected with the disappearances of well-known opponents of the president.
Police investigators and even members of the state security service have presented evidence that an official "death squad" was set up to eliminate opponents of the regime.
While Mr Lukashenko has angrily dismissed the allegations, those who made them have gone into hiding or fled Belarus.