The first thing to do is contact an experienced compensation lawyer. (Of course I was going to say that....) Second, if the lawyer is worth anything, he/she will know what to do.
In November 2006, the Pennsylvania's Workers' Compensation law was amended to create the Uninsured Employer Guaranty Fund.
You must file a Notice of Claim within 45 days after the employee learns that the employer does not have insurance. 34 Pa. Code 123.802. Here's a link to the Notice of Claim form: http://www.dli.state.pa.us/landi/lib/landi/bwc/libc-551.pdf
A claim petition may be filed against the Fund 21 days later. Here's a link to the specific form to be used: http://www.dli.state.pa.us/landi/lib/landi/bwc/libc-550.pdf
Here are the prerequisites for filing claim petition for benefits from Fund:
§ 123.803. Prerequisites for filing claim petition for benefits from Fund.
(a) Upon the filing of a completed ''Notice of Claim Against Uninsured Employer'' (Notice), the Uninsured Employer Guaranty Fund (Fund) will determine whether it will commence making payments.
(b) An injured worker may not seek an award against the Fund unless the worker completes and files the form designated as the ''Claim Petition for Benefits from the Uninsured Employer Guaranty Fund.''
(c) A ''Claim Petition for Benefits from the Uninsured Employer Guaranty Fund'' may not be filed until at least 21 days after the injured worker filed the Notice as required in § 123.802 (relating to notice to the Uninsured Employer Guaranty Fund).
(d) A completed ''Claim Petition for Benefits from the Uninsured Employer Guaranty Fund'' will be deemed filed upon the later of either of the following:
(1) The date of the petition's deposit in the United States Mail, as evidenced by a United States Postal Service postmark, properly addressed, with postage or charges prepaid; or, if no United States Postal Service Postmark is present, as of the Department's receipt of the petition.
(2) Twenty-one days after the filing of the Notice identified in § 123.802.
(e) The Department may reject any incomplete petition.