Hundreds of protesters have marched to NSW Parliament House to campaign against the shutdown of the state's greyhound racing industry.

Mr Baird announced the ban last month after a special commission of inquiry found overwhelming evidence of animal cruelty, including mass greyhound killings and live baiting.

After a party meeting yesterday, Upper House MP Peter Phelps became the first Liberal MP to voice his concerns about the ban, saying he did not think it was fair to "euthanase" an entire industry due to the malfeasance of a minority.

Several hundreds protesters, including many who travelled from across the state, gathered in Hyde Park with their dogs before marching to Parliament House.

Some of the protesters were holding placards depicting Premier Mike Baird as a dictator.

Crowds of protesters marched to NSW Parliament to call for Premier Mike Baird to reverse his decision to ban greyhound racing. ( ABC News: Nick Dole )

Today's protest comes after Greyhound Racing NSW asked a forensic investigator to look into new information concerning more possible greyhound grave sites similar to the one in the Hunter Valley where 99 dogs had been buried.

The NSW Liberal and National parties held a joint partyroom meeting on Tuesday to discuss the ban.

Several National MPs have already spoken out against the ban and Barwon MP Kevin Humphries said his opposition to the decision had not wavered.

He said while the legislation was yet to drafted, alternatives to the ban were discussed, but the arguments he heard did not change his opinion.

"Until you see the legislation you would be silly to make a comment on it, whether you would cross the floor or not," he said.

"But, generally I'm holding the line that if there is a ban and that is the thrust of it, then yes, I would oppose."

Ban a plan for 'mass slaughter': Foley

NSW Opposition Leader Luke Foley addressed the crowd, vowing to oppose the ban, and warned the closure of the industry would see greyhounds killed and burnt en masse.

"This is his plan for animal welfare. It's not a plan for animal welfare, it's a plan for mass slaughter," Mr Foley said.

He said the Government would have to engage a crematorium because the "greyhound carcasses will be piled sky-high and they'll have to burn them".

Crowds gathered in Sydney to protest against the NSW Government's decision. ( ABC News: Nick Dole )

"This is not the sort of thing we can accept in a free, democratic country, a shutdown of an industry worth $335 million to our state's economy every year."

He said the announcement was a "tyrannical measure masquerading as a humane gesture".

The Greens held a meeting at State Parliament for representatives of animal rescue groups which support the ban.

Greens MP Mehreen Faruqi said animal welfare groups and advocates had been working for the ban for decades.

She said the meeting came after two rallies in recent weeks which were attended by hundreds of supporters of the ban.

Animal welfare groups have voiced their support of the ban and have called for it to be made national.

The start of the protest march at Hyde Park with Robert Borsak, Reverend Fred Nile and Luke Foley. ( Supplied: Shooters, Fishers and Farmers Party )

Majority of greyhound owners 'absolutely love their dogs'

Noelene Holloway from Hamlyn Terrace, on the NSW central coast, travelled to Sydney to address Tuesday's rally.

She said her family had been racing greyhounds for more than 50 years and she wanted the industry to be saved for the sake of the dogs.

"The large majority of greyhound owners and trainers absolutely love their dogs," Ms Holloway said.

"I'm not actually fighting for my livelihood or anybody else's - I'm fighting for the life of the greyhound."

Ms Holloway said she remained optimistic about the future of the racing industry, despite the State Government's plan to shut it down next year.

She said the entire industry had been tarnished by a small few and the Government needed to recognise that.

"The truth is on our side. If what they were saying was true we would have to cop it but what they're saying is not true," Ms Holloway said.

"There's no evidence to back what they're banning our industry on."