Fontwell and Southwell are the latest tracks to be hit as trainers appear to have followed through on their threat of further boycott action against Arena Racing Company-owned venues.
A total of 27 runners will contest six races at Fontwell on Wednesday, while Southwell's six events on Thursday have drawn just 20 contenders - with each fixture featuring a match race.
Trainers had signalled their intention to take action over three days this week as they continue to battle with ARC over the operator's decision to cut back on its contributions to prize money at its 16 tracks nationwide.
It was announced in December that changes would be made as ARC prepares for an expected shortfall in the levy because of anticipated betting-shop closures following the Government's decision to lower the maximum FOBT stake from £100 to £2.
This decision has been met with dismay by many trainers, owners and jockeys, and the situation came to a head last month when two races at Lingfield were boycotted - with no runners declared in one and Nick Littmoden's Greybychoice enjoying a walkover in another.
Another race at Sedgefield on Sunday was reduced to a walkover, but there appeared to have been a positive development on Saturday evening when ARC and the National Trainers Federation issued a joint-statement - in which ARC committed to unlocking extra funds for all eligible races in March.
That announcement came after entries were made for Lingfield's Wednesday fixture, with 40 possibles duly reduced to just 17 runners at Monday's declaration deadline.
Only five jockeys are prepared to ride on the card, with a number of riders issuing a rallying call as they throw their weight behind the protest.
Nico De Boinville, Aidan Coleman and Gavin Sheehan are among a handful of of high-profile riders who will be in action at Fontwell on Wednesday.
De Boinville has stated the boycott has his backing, yet he feels he should ride Eglantier for Mark Bradstock and his fee will go to the Injured Jockeys' Fund.
The jockey tweeted: "I fully support the current ARC boycott. However, I feel obliged to ride for one of my main stables tomorrow. I will be donating my riding fee to the @IJF_official."
David Bridgwater sends out one of the two horses in the match race, as well as fielding a last-time-out winner in the opening handicap chase, and the handler is not getting involved in any boycott talk.
He said: "I've no view on it, I'm straight down the middle.
"(Ex-jockey) Philip Hide is the clerk of the course at Fontwell, he is an old friend and I like to support him.
"I've always had runners at Fontwell, it's a lovely track."
