The initiative - which supports people as they try a vegan diet throughout January - expects its biggest year ever in 2019, with an estimated 30,000 sign-ups.
And it's hoping that politicians will join members of the general public.
Vegan diet for the planet
"The Government has so far done little to heed the advice of the scientific community, which states that reducing meat and dairy consumption is vital if we are to avert catastrophic climate change," Veganuary said in a statement sent to Plant Based News.
"While the public appetite for everything vegan continues to skyrocket, this has not been matched by policy or political leadership.
Vegan diets tackling climate change
"Trying vegan for January by switching to tasty plant-based alternatives in the cafeterias of Parliament would be a simple step to take for our leaders to lead by example, and show they're serious about tackling climate change," Rich Hardy, Head of Campaigns at Veganuary, added.
"2018 was huge for bringing veganism out of counter-culture. But 2019 will be the year when it becomes a considered lifestyle choice for millions embracing cruelty-free, health living."
The charity will be campaigning outside Parliament today - with guerilla light projections calling on the Prime Minister to try vegan for January.