Tanzanians have so far raised more than $100,000 (£78,000) to help pay a fine of $150,000 handed down to nine opposition leaders found guilty of illegally holding a rally two years ago.
At the rally, a female student died after being hit by a stray police bullet, fired as officers tried to disperse the crowd.
Political rallies were banned by President John Magufuli after he came to office in 2015.
After their conviction on Tuesday, a campaign was started on Twitter to help raise funds.
The opposition Chadema party tweeted its thanks on Wednesday afternoon, saying 234m Tanzanian shillings ($102,000) had been raised in 24 hours
Meanwhile, a powerful US senate committee has criticised what it called “spurious charges” against the opposition leaders.
Their conviction was more evidence of the deteriorating political space and freedoms in Tanzania, the US Senate Foreign Relations Committee tweeted.
The government's efforts to criminalise the opposition further undermined the possibility of democratic elections later this year, it added.
The government denies such allegations.
"Tunawashukuru sana Watanzania kwa michango yao wanaoendelea kuchangia, kitendo cha kuchangia kufikisha Mil. 234 ndani ya saa 24 ni jambo kubwa sana. Bado tunahitaji michango zaidi iendelee ili kuweza kuwatoa viongozi wetu wote," Kaimu Katibu Mkuu wa @ChademaTz Kigaila Benson.
— CHADEMA Tanzania (@ChademaTz) March 11, 2020
The conviction of @ChademaTZ members, incl. @freemanmbowetz, on spurious charges, is more evidence of deteriorating political space & freedoms in #Tanzania. The govt's efforts to criminalize the opposition further undermines the possibility of democratic polls later this year.
— U.S. Senate Foreign Relations Committee (@SenateForeign) March 10, 2020
