One of the biggest risks to stock prices could be great news for American workers

Rising wages for American workers could be bad news for US stocks.

In a report to clients on Wednesday, Peter Sullivan and his team at HSBC took a look at the rising risk that higher wages for American workers could start eating away at the record profit margins and earnings growth that has been enjoyed by US corporations.

"Consensus earnings growth forecasts for the US are too optimistic in our view at 10% for 2016 and 13% for 2017 versus our forecast of 2% and 7% respectively," Sullivan writes. "Consensus is based on widening margins but we find this implausible given that we expect a pick-up in wage growth."

This year, one of the dominant economic themes has been the coming increase in wages for US workers. Early-year announcements from the likes of Wal-Mart, Target, and TJ Maxx indicated that retailers were starting to feel the squeeze from higher employee turnover and more abundant job openings.

Various readings like the employment cost index and average hourly earnings, however, have disappointed, with the ECI growing just 0.2% in the second quarter and average hourly earnings rising 2.2% in August, about the same as they've been rising over the last several years.

However, other measures like the Atlanta Fed's 3-month tracker of median wage growth indicate wages are up about 3.1% this year, the best since before the recession.

So, the data is mixed. But with the unemployment rate down at 5.1% and the number of jobs openings at the highest since at least 2000, most economists expect higher wages are finally coming for American workers.

And with this, companies will face rising costs in an area where they've enjoyed leverage for years.

HSBC noted on Wednesday that corporate profit margins in the US are already above average at around 13%, and while consensus expectations are for margins to increase, the firm expects margins will actually contract as a result of this increased wage pressure.

And so unless demand from both US and international consumers and customers beats HSBC's expectations, earnings and margins are due to decline.

As we've noted in recent days, earnings growth for US corporates is already on the decline, with 2015 set to be the first year since 2009 that earnings decline over the prior year.

And so this view from HSBC comes, then, as the latest in a series of warnings that the rapid increase in earnings and stock prices enjoyed by US companies in the last 5 years could be if not coming to an end, at least leveling off.