Users of the site have created the search term '#otscampaign' to discuss ways of lobbying the OTS to change its mind over the decision.
Thirty-two successful applicants to the programme, which aimed to help small charities advocate for change, were told last week that it no longer existed.
The funding has been diverted to the Hardship Fund, a £16.7m fund to support third sector organisations providing services for disadvantaged people during the recession. The OTS said the funding would provide 15 extra grants for the fund.
The decision was announced without consultation three weeks after the successful applicants to the campaigning fund had been told they would receive funds.
Messages posted on Twitter include: "Govt say it's ok to breach Compact? Steal from Peter to feed Paul while Goliath gets fat"; "Lack of logic: Cabinet Office cuts funds to 30 small organisations to help 15 small charities survive recession!"; and "Why cancel the campaigning fund now and so suddenly? What's happened to make it worth OTS breaching the Compact so blatantly?"
By Monday evening the campaigners had arranged to set up a list of the organisations that had lost out as a result of the decision.
Kevin Curley, chief executive of umbrella body Navca, has written a letter to Angela Smith, minister for the third sector, asking her to change her mind about reallocating the funding.
"If you had cancelled this programme before grants had been awarded we would have been less disturbed by the decision," it says. "But to cancel after grants have been awarded and without consultation will be seen in the local sector as an expression of the OTS's non-compliance with the Compact. We deeply regret that."