They protested at the "illegal nature'" of the poll in which he is seeking a constitution which would give him autocratic powers, including the right to appoint judges, top election officials, and many members of a new, two-chamber legislature. The protest, following expressions of alarm from the US, came as Belarus lumbered towards a showdown between the President and parliament and which has sent tremors from the Baltic to the Black Sea.
MPs, fearing Mr Lukashenko's security forces may close it, have been occupying parliament, in the capital, Minsk, since Friday. The Prime Minister, Mikhail Chigir, resigned in protest over the referendum.
Eighty MPs also signed a petition for the President's impeachment. Under the constitution (which Mr Lukashenko has a long record of ignoring), this must be approved by the Constitutional Court before going back to parliament, where it requires a two-thirds vote to pass.
While the West seethed, a more cautious expression of concern was issued by Russia, the key player in efforts to resolve the crisis. Moscow exerts great influence on the former Soviet republic, which depends on it for gas and oil. A Kremlin spokesman said President Boris Yeltsin and his Prime Minister, Viktor Chernomyrdin, were "alarmed" and hoped "the art of political compromise will replace the ambitions and confrontations among politicians".
Officially, voting day is Sunday, although the result is viewed as a foregone conclusion unless the poll is cancelled and a compromise is found. For there are signs aplenty that the President has little regard for fair play. He has fired the head of the Central Election Commission, Viktor Gonchar, who complained of irregularities among thousands of absentee ballots already cast.
For months Mr Lukashenko has excluded opponents from the heavily censored state-run media while using it to advertise his cause.
If he wins, a confrontation with parliament seems inevitable but the outcome is unclear. He has the loyalty of his 1,500-strong presidential guard but the position of Belarus's KGB and armed forces is less easily predicted. "There is potential for this to blow up," a Western source said. "It would only take one spark to set everything off." Last night parliament offered to abandon a second, parallel referendum which proposes the presidency be scrapped, if Mr Lukashenko dropped his. His response was unknown, but his posture to date is not encouraging.
He recently said it was too late to change his plans, and told opponents to be ready to flee if he won. His style has won him unfavourable publicity in the West, particularly when he complimented Hitler during a media interview.
Poland, Ukraine and the Baltic states have all shown signs of unease about their troublesome neighbour.
Nor are matters helped by the fact that Belarus still has 18 former Soviet SS-25 intercontinental missiles, which it is due - under international arms agreements - to return to Russia soon, but which it may seek to keep as bargaining tools.Reuse content