Section 48. Every employer of labor engaged in carrying on any manufacturing, mechanical or mercantile establishment or workshop in the commonwealth shall allow every person, except those specified in section fifty, but including watchmen and employees maintaining fires, employed in such manufacturing, mechanical or mercantile establishment or workshop at least twenty-four consecutive hours of rest, which shall include an unbroken period comprising the hours between eight o’clock in the morning and five o’clock in the evening, in every seven consecutive days. No employer shall operate any such manufacturing, mechanical or mercantile establishment or workshop on Sunday unless he has complied with section fifty-one. Whoever violates this section shall be punished by a fine of three hundred dollars.