Google fired another employee activist on Friday, the fifth termination of an employee engaged in workplace organizing in less than a month.

Kathryn Spiers, a 21-year-old security engineer who had worked for Google since February 2018, was suspended from work on 25 November – the same day that four other worker activists were fired for what the company described as “intentional and often repeated violations of our longstanding data security policies”.

Her suspension began just three hours after she published a piece of code that created a pop-up notification when Google employees visited the website of IRI Consultants, an anti-union firm that it was revealed Google had hired just a few days earlier.

Kathryn Spiers, a security engineer who had worked for Google since February 2018, was fired on 13 December. Photograph: The Guardian

“Googlers have the right to participate in protected concerted activities,” read the browser notification, which appeared on the bottom right-hand corner of the site and was visible only to Google’s own workforce.

“I had been involved in other workplace organizing in the past, but the reason I wanted to push this change was a combination of Google hiring IRI and four of my co-workers being fired the same day,” Spiers said in an interview on Monday. “I thought a lot of my co-workers could use a reminder of their rights.”

Spiers remained on suspension until 13 December, when she was informed of her termination by phone call, she said. A Google spokeswoman said the company had dismissed an employee who had “abused privileged access to modify an internal security tool”, which was “a serious violation”.

On Monday, Spiers filed a complaint with the National Labor Relations Board (NLRB) alleging that her firing was an unlawful response to workplace organizing activity, which is protected by federal labor law. The other four fired workers also filed similar charges, known as an unfair labor practice, with the labor board. At the time, Google said, “No one has been dismissed for raising concerns or debating the company’s activities.”

After publication of this article, Google shared a copy of an email from Royal Hansen, an executive for Spiers’ team, in which he confirmed her identity and characterized the pop-up tool as an “unacceptable breach of a trusted responsibility”. “The issue was not that the messaging had to do with the NLRB notice or workers rights,” he added.

“Of the five people that were fired, three of us are trans women,” Spiers said. “That is either an unbelievable coincidence or Google is targeting the most vulnerable.”

“Trans Googlers make up a very small percentage of Googlers,” she added. “They make up a slightly larger percentage of organizers, but not 60%.”

Spiers’ work on Google’s platform security team often included writing browser notifications that would appear on certain sites when her co-workers were using the internet. If a Google employee navigates to Dropbox.com, for example, a browser notification will pop up reminding them not to upload confidential documents.

Spiers was also involved in a protest of a corporate crackdown on open access to internal documents. Historically, Google employees were empowered to look at almost any document in the company’s vast intranet. Amid recent labor unrest, however, the company’s chief legal officer, Kent Walker, has pushed for restricting access to more information on a “need-to-know” basis, Bloomberg reported.

The policy change has prompted significant backlash, and Spiers participated in writing code for an internal browser extension that allowed Googlers to send Walker an automatic email asking whether a document was “need-to-know” every time they attempted to open any document. The browser extension was first reported by Bloomberg.

“The goal was not to make his email too cluttered to use,” she said. “It was to show that Googlers thought the policy was too vague and harmful to our getting our jobs done.”

Google was once exalted for having one of the happiest workforces in the world, but the company has been roiled by increasingly bitter disputes between employees and executives over the past two years. Internal debates over issues ranging from the tech industry’s lack of diversity to the ethics of providing a censored search engine in China have burst into the open through leaks to the press, increasing public pressure on the company.

The four workers fired in November all denied ever having leaked information externally.

Employees have also become more organized and outspoken. Following the revelation that Google had given its former executive Andy Rubin a $90m severance package when he left the company following an allegation of sexual assault, approximately 20,000 Googlers staged a global “walkout for real change”. Googlers have published a steady stream of petitions calling on their employer to change course on issues including climate change, providing services to US immigration enforcement agencies and treatment of temporary and contract workers.

Several of the organizers of the walkout left the company earlier this year, alleging retaliation for their roles in the protest. Google denies that it engages in retaliation.

“A lot of the reason I trusted Google is because I know there are people like me all throughout the company that are watching for abuses,” Spiers said. “The changes that Google is making are making the company less transparent, and I think that is making Google less trustworthy and less secure.”