Activist Okiya Omtatah last Friday moved to court to challenge Finance Act, 2018, which Members of Parliament passed the previous day amid outcry.
As Mr Omtatah, the Executive Director of Kenyans for Justice and Development Trust, filed the case, Kenyans online started a campaign to fundraise for him.
Those who started the initiative urged the public to send him as low as Sh10 for photocopies, transport and the filing of the cases.
On Twitter, @KinyanBoy wrote: If there's one man that has stood with Kenyans in times of injustice, it is one man called Okiya Omtatah. For this reason I'm joining the initiative to finance his work. If every Kenyan sent Sh10 only, he'd be at Sh400M+. M-Pesa anything to Andrew Okoiti, 0722 684777 [sic]."
One Jerotich Seii said: "Having run out of things to tax, it is only a matter of time before Ushuru Kenyattax goes after our contributions to this courageous Kenyan hero. Please support Okiya Omtatah via M-Pesa as he continues to fight for us."
Mr Omtatah wants the court to determine the validity of the decision by National Assembly Speaker Justin Muturi, to determine the fate of the Finance Bill, 2018 by acclamation and not division of the vote.
He said the Constitution requires a special majority to determine the issue.
The activist has sued the Speaker and Attorney General.
Mr Omtatah also wants the court to determine whether the power in the Constitution, for the President to veto a Bill passed by Parliament, empowers him to legislate using a one-third minority of MPs.
The petition also seeks to know the fate of a Bill returned to Parliament by the President, where Parliament partially or fully rejects the reservations but fails to garner the two thirds majority to override the reservations.
MPs had voted to suspend the implementation of the Bill for another two years but President Kenyatta returned it to Parliament with reservations.
To overturn President Kenyatta's reservations, some 233 MPs needed to reject it.
Mr Omtatah wants the court to declare Finance Act 2018, which was passed by acclamation and not by division of the vote, unconstitutional and therefore invalid, null and void.
He also wants the court to declare that the president has no powers to legislate and that his veto powers are limited to expressing his reservations, not proposing amendments to Bills.
"Since the president does not have any legislative authority, reservations in his memorandum cannot purport to amend the rejected Bill. The president must return the Bill to Parliament with a memorandum expressing his reservations, not proposed amendments. The president has no power to propose amendments," he argues.
Mr Omtatah also argues that having embraced the principle of separation of powers in Article 1(3), it is untenable that the drafters of the Constitution could have intended that the memorandum containing the president's reservations should override Article 94 which vests legislative authority upon Parliament.