More than 300 security guards at Harvard are awaiting new uniforms and a new employer as Allied Security prepares to acquire Security Services Inc. (SSI) on March. 19.

The acquisition has yet to be finalized, according to Allied Security spokesperson Larry Rubin.

“We hope that [SSI] will accept the contract as it is written, but there is the possibility of changes,” Rubin said.

But even though the agreement has not been set in stone, some workers are already uneasy about the change.

In a letter sent to its soon-to-be employees last week, Allied Security promised that wages will remain the same and that workers’ seniority at SSI will be transferred to Allied Security.

According to SSI employees, Allied Security told workers that they will have to go through the motions of reapplying for their jobs, but assured them that all will be rehired in the same positions.

SSI employees not at Harvard, however, will not be guaranteed their old jobs in the reapplication process.

“The University has been assured that there will as smooth a transition as possible,” said Merry Touborg, a spokesperson for Harvard’s Office of Human Resources. “The University has let both companies know that we are concerned about any security disruptions.”

Touborg said both companies informed Harvard of the pending transaction.

SSI, a local company based in Malden, Mass., provides security to Harvard’s Medical, Law and Business Schools, as well as to the River Houses and the Yard. Allied Security, which bills itself as the third-largest security company in the country, currently has a small force staffing the security desk at Holyoke Center.

One SSI worker, who asked not to be identified, said the sale took him by surprise.

“I’m not in the CEO’s mind, but we were surprised because we were doing really good,” he said.

SSI won contracts to secure a number of new sites at Harvard last May, including the Science Center and various science labs.

SSI Operating Manager Robert Taylor did not return calls requesting comment yesterday.

Allied Security held orientations for SSI workers in Boston last weekend to familiarize them with the policies of the company.