Technically it is also a violation of your safety policy as well, and if something happened to them your company would get a fine.
110.1 Relationships with Contractors (Outside Service Personnel, etc.).
(A) Host Employer Responsibilities.
(1) The host employer shall inform contract employers of:
a. Known hazards that are covered by this standard, that are related to the contract employer?s work, and that might not be recognized by the contract employer or its employees
b. Information about the employer?s installation that the contract employer needs to make the assessments required by Chapter 1
(2) The host employer shall report observed contractemployer- related violations of this standard to the contract employer.
(B) Contract Employer Responsibilities.
(1) The contract employer shall ensure that each of his or her employees is instructed in the hazards communicated to the contract employer by the host employer. This instruction is in addition to the basic training required by this standard.
(2) The contract employer shall ensure that each of his or her employees follows the work practices required by this standard and safety-related work rules required by the host employer.
(3) The contract employer shall advise the host employer of:
a. Any unique hazards presented by the contract employer?s work,
b. Any unanticipated hazards found during the contract employer?s work that the host employer did not mention, and
c. The measures the contractor took to correct any violations reported by the host employer under paragraph (A)(2) of this section and to prevent such
violation from recurring in the future.