The issue was most pronounced at the smallest and largest employers, the report found. 77 percent of people working in start-ups and 78 percent of those at companies with more than 10,000 employees said they were avoiding tough conversations, compared with around 60 percent of people at medium-sized companies.

Toby Hervey, CEO of Bravely, said that could be the result of a lack of access to HR or, particularly at smaller firms, a suitable representative.

A problem for start-ups and big business

"At small companies, relationships can be generally more intensive (you spend a lot of time with a small number of colleagues!) and that can make it harder to create the space and time for difficult conversations and sharing tough feedback," Hervey told CNBC Make It in an email, noting that smaller firms typically have limited — or non-existent — HR departments.

"We've seen in some organizations that some employees may not know who their designated HR contact is," Hervey added of larger organizations. "If they do, many HR representatives are supporting hundreds, if not thousands, of employees, and can have minimal bandwidth."

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That said, the report also pointed to a reluctance among employees to call on their HR departments in times of difficulty. Just 19 percent of respondents said they would go to their HR department with an issue.

"Going to HR feels like a step that can't be taken back," noted Hervey. "People perceive that there is a lot of preparation and confidence needed (and) that can be intimidating and enough to make people think that it would be easier to avoid the conversation altogether," he said, adding that past bad experiences can also make people more reluctant to call on HR in future.

New work trends are fueling the problem

Bravely's research follows a 2009 study into the avoidance of "scary" workplace conversations. Despite the 10-year gap and billions of dollars businesses have invested in people development over that time, the reports recorded the same 70 percent gap.

"The study revealed that the same challenges have persisted over the last decade, and even nods to new compounding factors that have complicated the conversation gap over time," said Hervey.

Those compounding factors include the rise of remote working, which has created geographic impediments, and the advent of job rating sites, which have made it easier for employees to complain anonymously. People who admitted to staying silent were eight times more likely to post a negative review on a site like Glassdoor, according to Bravely's study.

A strong U.S. jobs market has also made it easier for employees to "jump ship" instead of facing issues at their current workplace.

How to approach a difficult conversation?

Nevertheless, approaching difficult conversations is not only an important workplace skill, it could also be what enables your next step forward, said Sarah Sheehan, Bravely's chief customer officer, who co-founded the company with Hervey as a platform for confidential professional advice.

She outlined three tips to prepare yourself for a difficult conversation at work.

1. Consider viewpoints beyond your own

"It's easy to think about yourself and only yourself when you're dealing with something challenging at work, but take the time to think through how someone might see it from the other side, and whether certain circumstances could be creating the situation at hand," said Sheehan.

Your manager is a person, too, noted Sheehan, so sometimes the best thing you can do is to put yourself in their shoes and try to think things through from a new perspective.

2. Expect the best, but prepare for the worst

While you will be hoping for the best possible resolution to your conversation, it's helpful to prepare yourself for a potential negative outcome. That way, you will be better able to keep your emotions in check and avoid escalating the situation, Sheehan noted.

"Try to think through the worst-case scenarios and prepare for how you might respond in that situation. That way, you might be less likely to react with emotion," she said.

3. Say it out loud

Finally, try rehearsing the conversation, either to yourself or someone else, to hone your message and perfect your delivery, said Sheehan.

"It will no doubt feel awkward at first," she said, adding that "forcing yourself to say the words will help you hone how you deliver it, control the tone (which is super important!), and ensure you stick the landing."

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