MADRID, July 1 (Reuters) - Spain"s competition watchdog CNMC is investigating possible anti-competitive practices in Spain by Apple Inc (AAPL.O) and Amazon.com Inc (AMZN.O) regarding online sales of electronic products. The CNMC said in a statement on Thursday that it had opened disciplinary proceedings over possible unlawful conduct by both companies that would include possible restrictions on the Amazon website in Spain. "(Restrictions) would affect the retail sale of Apple products by third parties and the advertising of competing Apple products, leading to a reduced competition in the Internet retail market for electronic products," the CNMC said. In addition, they could strengthen Amazon"s position in the sector of providing marketing services to third-party retailers through online platforms in Spain. Amazon said in a statement it was fully collaborating with the authority on this issue, while Apple in Spain was not immediately available to comment. The CNMC"s proceedings open a maximum period of 18 months for the investigation and resolution of the case.