Essex have joined Middlesex in announcing they will refuse to endorse the England and Wales Cricket Board's proposed eight-team Twenty20 competition.
The ECB is pressing for constitutional change required for the city-based tournament, planned to commence in 2020, which would not involve all 18 first-class counties.
And while many of them have come out in support of the plans, with Durham the latest to do so on Wednesday, Essex became only the second to voice their disapproval.
ECB chairman Colin Graves identified a "watershed moment" last month when he triggered a postal ballot to support the amendment to the national governing body's articles of association.
The vote involving all 18 first-class counties, the MCC, Minor Counties Cricket Association and 21 recreational boards must be concluded within 28 days.
Essex chairman John Faragher said: "We do not support the changes to the articles of association and consequently the proposed new T20 competition. It is essential that the County Championship, domestic 50-over and T20 competitions are encouraged to grow, and they must be protected.
"We recognise and support the Cricket Unleashed Strategy and indeed Essex County Cricket Club has an enviable record in producing England players and captains.
"We are focused on expanding cricket in Essex, East Anglia and Metropolitan London, ensuring there are opportunities for all age and ability groups, male and female, to be actively involved in the game.
"We believe that as a result of the proposed changes, these opportunities will be reduced, that our income overall will suffer and the first-class game will be diminished, in contradiction to the ECB's objective which is to grow the game in this country - an objective that is unlikely to be advanced by a competition which would exclude large areas of the country from any involvement in it."
Since the ECB's executive board resolved to dispatch the paperwork on March 28, indications were of favourable response - with Middlesex first to break ranks before Essex did so on Wednesday.
Sussex, Somerset, Yorkshire, Derbyshire and Leicestershire have all given their endorsements, while Durham's backing followed a members' meeting on Tuesday evening.
Chairman Sir Ian Botham said: "The competition is exciting and offers a number of positive opportunities. We will hopefully be very much part of it and do our best make the tournament a huge success.
"It's financially very sensible to do it and if we prepare properly and come up with the right formula throughout the summer - just look at the success of the Big Bash in Australia and the IPL - then it's proven that the format has great benefit.
"I would have loved to have played the competition myself. It's total entertainment. I see the T20 format as a vehicle to bring people back into the grounds. The flagship should always be Test cricket, as that's the ultimate challenge but T20 has its place.
"You want to see kids and young people at sold-out cricket grounds and I think the new competition will help do that alongside the NatWest T20 Blast."
Each club will receive a Â£1.3million annual share of the new competition's revenue in its first four years, and to proceed the ECB needs a vote of at least 31 in favour from the 41 member organisations consulted.