According to Article 223(2) TFEU, the European Parliament lays down regulations and general conditions governing the performance of the duties of its Members. It needs the consent of the Council and an opinion from the Commission.
The main act is the Statute for Members of the European Parliament, more exactly:
DECISION OF THE EUROPEAN PARLIAMENT 2005/684/EC, Euratom of 28 September 2005 adopting the Statute for Members of the European Parliament; OJEU 7.10.2005 L 262/1
Then there is an implementing Bureau decision with the nitty-gritty euro stuff, which follows the annoying practice of not being identifiable and traceable by number:
DECISION OF THE BUREAU of 19 May and 9 July 2008 concerning implementing measures for the Statute for Members of the European Parliament; OJEU 13.7.2009 C 159/1
The EP Bureau has now published a batch of amendments in the Official Journal of the European Union, still without an easily identifiable number for its decision:
DECISION OF THE BUREAU OF THE EUROPEAN PARLIAMENT of 11 and 23 November 2009, 14 December 2009, 19 April 2010 and 5 July 2010 amending the Implementing Measures for the Statute for Members of the European Parliament; OJEU 6.7.2010 C 180/1
Formally, the decision enters into force tomorrow, but in practice a number of the reimbursement practices have already become effective.
In its own affairs, EP practices are still not quite up to scratch.