It is felt that the original certificates of the employee are property of the employee and no employer can have any lien on it.
The employee can offer to provide attested/notarized copies and even show the original for the purpose of marking OSV by employer. The employee should not surrender himself/herself and fall in a situation where he /she should have to compromise later and feel enslaved.
This is a trend which is being started by employers to retain the originals. In case an issue crops up employee may have to resort to litigation to get back his own certificates.
Even if the company is willing to provide acknowledgment of the originals you may offer to provide the attested/notarized copies and show original for marking OSV.
A reasonable employer should be satisfied with it.
Ask them to issue a communication to you in writing expressing the intention of employer to hold your originals.
Although company is willing to issue acknowledgment it may not agree to issue a written demand for keeping originals.
You may evaluate your choices, and proceed as deemed fit.
Valuable advice of learned experts/members is sought.