however, a frontier worker who is posted elsewhere in the territory of the same or another Member State by the undertaking to which he is normally attached and is prevented on account of such posting from returning daily or at least once a week to the place where he resides shall nevertheless retain the status of frontier worker for a period not exceeding four months;

Allowances specific to the posting shall be considered to be part of the minimum wage, unless they are paid in reimbursement of expenditure actually incurred on account of the posting, such as expenditure on travel, board and lodging.

post workers to the territory of a Member State on their account and under their direction, under a contract concluded between the undertaking making the posting and the party for whom the services are intended, operating in that Member State, provided there is an employment relationship between the undertaking making the posting and the worker during the period of posting;