A bitter firefighters' feud that has split Daniel Andrews' cabinet spilled onto Melbourne's CBD on Saturday, with CFA volunteers protesting at Parliament in a bid to stop the Premier caving in to union demands.

Under grey skies shortly after midday, a motorcade of 421 fire vehicles made its way to Spring Street to join volunteers who fear the government is about to sell out to the United Firefighters Union.

A motorcade of about 250 CFA trucks hit Melbourne streets on Saturday in protest over fears of a secret deal between the state government and the firefighters union. Credit:Chris Hopkins

The rally was called amid claims that the Premier had struck a "secret deal" with the union to hand over significant control of Country Fire Authority operations, and was about to capitulate to a raft of UFU demands, including a 19 per cent pay rise, a $3000 sign-on bonus, and a number of other generous allowances.

While the government has denied a deal has been done, concerns emerged after Mr Andrews met with union boss Peter Marshall last week to discuss the year-long industrial stoush, in a move that sidelined Emergency Services Minister Jane Garrett and divided his cabinet.