Nearly 20 civil society organisations have planned a demonstration calling for reform ahead of the 2018 elections.
Around 150,000 citizens, including Movement for Democratic Change (MDC) leader Morgan Tsvangirai, also expected to join.
Ncube says the #Thisflag Movement has united the country.
"The problem that Zimbabwe has, the selective application of the law. Zanu-PF is a player and it’s a referee, it’s a judge, it’s a prosecutor and everything else. We can’t allow this happen, Zimbabwe needs a new political culture."
MDC secretary general Douglas Mwonzora said a High Court judge will hear the case at 8 am on Friday, hours before the planned march.
Police used teargas and water cannon on Wednesday to break-up a march by MDC youth supporters, who were protesting against economic woes and what they say is brutality by security agents.
Police commander for the Harare Central District, Chief Superintendent Newbert Saunyama, told protest organisers in a letter on Thursday that they could present a petition at the Zimbabwe Electoral Commission without marching, adding that the expected number of participants, 150,000, was too big.
