The shareholder advisory group, Pensions and Investment Research Consultants (PIRC), is urging investors in Wetherspoon to oppose its annual report after questions were raised over the political spending in 2016.
Wetherspoon's chairman, Tim Martin, is an outspoken supporter of Brexit and made several high-profile statements in support of the Leave campaign in 2016.
He has regularly used his own pubs as a platform, distributing published material and giving speeches to argue the case for leaving the EU in pubs throughout the country.
Martin owns 32% of the pub chain. The rest is owned by institutional investors.
Although the pub chain declared its political spending to the Electoral Commission, PIRC argues that it should also have declared it in the annual report, given the threshold for telling shareholders about its annual political spending is just £2000.
PIRC has quoted legal experts who argue that shareholders should approve any activities "capable of being reasonably regarded as intended to influence voters in relation to any national or regional referendum".
The advisory body also says that the pub chain has weak policies on sustainability, and recommended that shareholders vote against the annual report on those grounds as well.
When asked for comment by the Guardian, Martin responded, "PIRC rhymes with berk".
Wetherspoon disputes PIRC's interpretation of the law, saying that the chain was not required to seek investors' backing.