WASHINGTON — A law to make marijuana possession in the District of Columbia punishable by only a $25 ticket, one of the laxest drug laws in the nation, has ignited a feud between Washington’s mayor and a Republican House member days before it is to take effect.

Mayor Vincent C. Gray urged district residents to boycott the beaches and resort towns of Maryland’s Eastern Shore, after its congressman moved to block the city’s marijuana-friendly law, claiming more teenagers will take up drug use.

“He is interfering with democracy in this city, and we want people to understand how we feel about it,” the mayor said in an interview. He pointed out that Maryland, like the district, decriminalized marijuana this year, and if the congressman, Representative Andy Harris, had been in the legislature, he would have been outvoted.

Marijuana has potent political symbolism in this city with a large black population because the vast majority of arrests here for possession is of blacks. But at issue is more than marijuana. Infringements on Washington’s home rule hits an ever-sensitive nerve, setting off howls of “hypocrisy” and “tyranny” in a city whose license plates read “Taxation Without Representation.”