Will New Job Prevent FHA Approval?

My husband and I are applying for an FHA loan of $180,000 and were pre-approved for this amount when my husband was making $2/hr. less. We are concerned about not being approved due to my husband having started a new job. Though the position is within the same field and he's making more money we are concerned b/c he gained the position through a temp agency under the condition that the position is temp to perm but because of contractual constraints between the temp agency and the client (company with whom my husband reports) they were unable to supply a letter confirming the date with which he would become permanent. They did however supply a letter confirming that the position is longterm. Should we be concerned that we will not get approved because they could not supply an exact date of permanent hire? And is there anything that we could possibly supply to further solidify my husband's income since they can't give him a firm date?