(Reuters) - Smaller ad-tech firms are raising competition concerns over Google's (GOOGL.O), opens new tab long-brewing cookies alternative, Privacy Sandbox, at a time when the internet giant's digital ads business is already under U.S. and UK scrutiny.

The US and UK regulators suspect that Privacy Sandbox, which has been in the making for five years, could give Google too much control over the digital advertising market, harming competition.Google's dominance through Chrome and Android platforms, which command the lion's share of internet users, makes adapting to Privacy Sandbox a critical necessity for ad-tech firms.

However, the investigations and potential technology development delays are hurting smaller ad-tech firms, as the burgeoning costs due to adoption delays for Privacy Sandbox will put them at a disadvantage against well-heeled rivals.

At least 11 ad executives told Reuters that Privacy Sandbox may create an uneven playing field that favors larger firms with greater funding and technical prowess.

Privacy Sandbox is a set of technologies that aims to enhance user privacy by anonymizing data, implementing stricter access controls, and targeting groups of users rather than individuals. It was developed to replace cookies, which are used for tracking and targeting individual users.

Google's initial plan to phase out third-party cookies in Chrome and replace them with the Privacy Sandbox met with significant opposition from ad-tech companies and antitrust regulators, compelling the search giant to backtrack.

"We've designed and implemented the Privacy Sandbox to support a competitive and thriving marketplace," the internet giant said, adding that Google has seen the ad industry investing in solutions to move away from third-party cookies.

AN UNEVEN PLAYING FIELD

"Smaller ad-tech companies simply do not have the engineering teams or financial resources to effectively build out functional Privacy Sandbox platforms that can be used at scale - they are at a complete disadvantage," said Drew Stein, CEO of ad-tech firm Audigent.

The firms face greater financial risk as Privacy Sandbox's uncertain timeline extends development costs beyond the initial $5 million to $10 million investment they had expected.

Stein said Audigent, which helps advertisers improve ad targeting and publishers boost ad revenue, has invested "several million dollars" into Privacy Sandbox over the past few years, representing a substantial investment considering its annual revenue of about $150 million.

Meanwhile, large firms such as Raptive and Index Exchange have invested less than 3% of their revenue towards engineering resources for Privacy Sandbox, according to sources familiar with the matter.

"Having a whole developers' team, spending multiple years on a project is a huge investment for a small-medium sized company," said Luckey Harpley, staff product manager at Remerge.

Experts said while larger ad-tech firms such as Taboola and Index Exchange might be less impacted by the introduction of the new technologies, regulatory efforts to ensure fair competition will be crucial in preventing Google from further consolidating its dominant position.

"I don't think Google's going to wind up in the sort of kingpin position that some people might say it will," said Dennis Buchheim, CTO at ThinkMedium and former CEO of IAB Tech Lab.

"Don't think it's going to be allowed."