Movement for Democratic Change leader Morgan Tsvangirai supports the boycott campaign in the face of division in his party. Last week, the MDC national council voted in favor of taking part in the poll.
Mr. Tsvangirai overruled participation in the vote and has since told the country's electoral commission that any member of his party who defies him and runs for election should be considered an independent.
But party Deputy Secretary General, Gift Chimanikire, instructed provincial officials to choose candidates for the poll.
The MDC was opposed to the re-introduction of the upper chamber that was abolished more than 10 years ago. But the ruling Zanu-PF party pushed a constitutional amendment allowing the change through parliament, where it enjoys a two-thirds majority.
Mr. Tsvangirai says he is opposed to the senate election because the electoral playing field is heavily tilted in favor of the ruling party, which in his words "provides for pre-determined results."
The six-year-old MDC has challenged the results of parliamentary elections of 2000 and 2005 and the presidential elections of 2002, citing vote rigging and violence by President Robert Mugabe's ruling Zanu-PF Party.
Mr. Tsvangirai's spokesperson, William Bango, is quoted by the South African Press Association news agency as saying Mr. Tsvangirai is confident he will get the support of the provinces.
Meanwhile, Mr. Mugabe told Zimbabweans studying in Italy that the poll will go on, with or without the MDC. Mr. Mugabe is in Rome, where he is attending the 60th anniversary of the Food and Agricultural Organization.