David Cumming, head of equities at Standard Life, said his firm "could not justify" pay going any higher.
Investors must do more to signal their unhappiness, he told the BBC.
It comes after Theresa May said corporate pay was excessive, and issued a green paper with ideas to curb it.
Mr Cumming told the BBC's Today programme: "We continue to see too many proposals that would bring a substantial increase [in pay], and we have to signal that we are not happy with that."
Blackrock, the giant American investment fund, has already written to public company bosses saying it would vote down proposals for excessive pay or pension perks.
Fund manager fires fat cat warning shot
Top pay under fire on 'Fat Cat Wednesday'
The BBC understands that, last month, 13 of the City's top fund managers met to discuss the issue.
Previous attempts to enforce boardroom restraint have foundered because shareholders have not been able to speak with a single voice.
But Mr Cumming said that this time round there was likely to be a more united front.
"We do speak to each other, and there is a general view that there are too many chairman who take too obsequious a view of their chief executive and their pay," he said.
Mr Cumming also hinted that the City was fearful of what might happen if it did not succeed in bringing pay to heel.
"If we don't succeed, then we might have much more draconian action from the government, which would be much less flexible and worse overall for shareholders," he said.
His warning was echoed by another fund manager, Colin McLean, managing director of SVM Asset Management.
He said that anger over large financial rewards could come to a head this year, with nearly half of FTSE 100 companies facing binding votes on pay.
"2017 could finally be a year for change in executive pay, with both investors and politicians ready for a fight," Mr McLean said.
He added: "Some long-term incentives were put in place before the 2012 reforms, with binding shareholder votes only required every three years.
"This year almost half the FTSE 100 face binding votes on pay, and we will see changes bite. The shareholder revolt seems less likely to fizzle out this time."
Executive pay is already "too high" and investors are ready to take a tough line with firms that present plans to boost bosses' remuneration, one of the City's top fund managers has warned.