It is being staged by opponents of fox hunting in response to the Conservative manifesto pledge of a free vote on repealing the ban.
Campaigners were gathering in City Square from 1pm before marching through the streets with placards.
West Yorkshire Metro said bus services were likely to be delayed as a result.
West Yorkshire Hunt Saboteurs said the emergency protest had been called in light of Theresa May’s recent comments in favour of fox hunting and her ‘threats’ to repeal the Hunting Act.
Its event page on Facebook explained: “The Hunting Act needs strengthening, not repealing! We encourage people to bring placards and musical instruments - let’s make a noise for the foxes, and other wild animals, who suffer persecution by thugs on horseback!”
The protest will followed by a vegan barbecue and drinks at Wharf Chambers to raise money for the group.