By Marcin Goettig
WARSAW (Reuters) - Poland's transport minister, a close ally of Prime Minister Donald Tusk, resigned on Friday after prosecutors said he may have broken the law by failing to declare his ownership of a $6,600 wristwatch.
Tusk told reporters he had accepted Slawomir Nowak's resignation, though he said he would welcome him back to his old job if the investigation cleared him of any wrong-doing.
Nowak, 38, had been tipped by some as a future prime minister. Earlier this year, Polish media reported on how he had a fondness for wearing expensive watches, including Swiss brands such as Hublot and Ulysse Nardin.
At the time, Nowak denied any wrongdoing and said that the watches had been loaned to him or were gifts from his family.
The allegations could dent the reputation for probity that Tusk's government has established. The government's popularity has been falling in recent months, according to opinion polls.
On Friday, the prosecutor's office said it had written to parliament saying there was "justified suspicion" that Nowak had broken the law by failing to disclose ownership of the watch.
"In the course of the investigation it has been determined that Slawomir Nowak has owned a watch purchased for the amount of 20,500 zlotys ($6,600)," the district prosecutor's office said in a statement.
Nowak is a member of parliament and so has immunity from prosecution. Prosecutors can only take him to court if parliament votes to strip him of his immunity.
Nowak is required by law to disclose all belongings which have a value above 10,000 zlotys. Nowak made no public comment on Friday and the transport ministry declined to comment.
($1 = 3.1074 Polish zlotys)
(Editing by Gareth Jones)