Just 13.6% of working film directors in the UK are women, new research has revealed.
A report commissioned by Directors UK also showed that the percentage of UK films directed exclusively by women has barely changed in 10 years, rising from 11.3% in 2005 to 11.9% in 2014.
The professional association has called for the film industry to take action on gender inequality by ensuring that half of all publicly-funded films are directed by women by 2020.
The group wants films to meet diversity criteria, which would include gender factors, before they receive government funding.
Beryl Richards, chairwoman of Directors UK said: "It cannot be acceptable that in 2016 any industry with this level of inequality continues to go unchecked - not least the film industry that plays such an influential role in our economy, our society and our culture.
"The first step to tackling this is by understanding why these disparities are happening in the industry.
"With such comprehensive evidence we can now pinpoint and address the areas that need the most attention and focus on rectifying it.
"Our suggestion of a 50:50 split in public funding is something that has been achieved in other countries, such as Sweden.
"Equality of opportunity in UK film-making is something we should all be working towards."
Despite 50.1% of film students and 49.4% of new entrants to the industry being women, just 21.7% of publicly funded films had a female director in 2014 - a figure that has dropped from 32.9% in 2008.
Directors UK blames in part a lack of a regulatory system to effectively monitor and enforce gender equality in the industry.
The report found that existing gender inequality creates a vicious cycle in which new female talent is discouraged by a lack of role models, leading to a smaller pool of female directors.
Sarah Gavron, the director of the 2015 film Suffragette about the fight for women's right to vote which starred Carey Mulligan and Meryl Streep, said the figures were "shocking and startling".
She said: "Film of course influences our culture which is why it is vital to have diversity and more gender equality both in front of and behind the camera.
"We need to work to shift this imbalance, and it seems the only way to do this is to be radical, rather than waiting for something to change."